🕷️ Crawler Inspector

URL Lookup

Direct Parameter Lookup

Raw Queries and Responses

1. Shard Calculation

Query:

Response:

Calculated Shard: 70 (from laksa059)

2. Crawled Status Check

Query:

curl -X POST \
  'http://laksa070.int.ahrefs:8124/' \
  -H 'Content-Type: text/plain' \
  -H 'X-ClickHouse-Database: crawler3' \
  -H 'Authorization: Basic YXBpOg==' \
  -d 'SELECT getAhrefsURLFromUnparsed(src_unparsed) AS found_url, ifNull(toUnixTimestamp(download_stamp), 0) AS crawl_time, ifNull(toUnixTimestamp(props_url_first_seen), 0) AS first_indexed_time, download_http_code AS http_code, src_unparsed AS src_unparsed, src_root_hash AS src_root_hash, history_drop_reason AS history_drop_reason, meta_title AS meta_title, meta_descriptions AS meta_descriptions, attrs_boilerpipe_text AS attrs_boilerpipe_text, attrs_markdown AS attrs_markdown, attrs_readable_markdown AS attrs_readable_markdown, meta_canonical AS meta_canonical FROM crawler3.page_info_local FINAL PREWHERE (src_root_hash, src_unparsed) IN ((getAhrefsRootHashFromUnparsed(getAhrefsUnparsedNoserviceFromURL(\'https://codeforces.com/blog/entry/52697\')), getAhrefsUnparsedNoserviceFromURL(\'https://codeforces.com/blog/entry/52697\'))) FORMAT JSONEachRow'

Response:

{"found_url":"https:\/\/codeforces.com\/blog\/entry\/52697","crawl_time":1775112309,"first_indexed_time":1545256399,"http_code":200,"src_unparsed":"com,codeforces!\/blog\/entry\/52697 s443","src_root_hash":"17282934374156394870","history_drop_reason":null,"meta_title":"Hashing: How to pick base and mod? - Codeforces","meta_descriptions":["Codeforces. Programming competitions and contests, programming community"],"attrs_boilerpipe_text":"→ Pay attention\n→ Top rated\n#\nUser\nRating\n1\nB\nenq\n3792\n2\nt\nourist\n3755\n3\ne\ncnerwala\n3696\n4\nV\nivaciousAubergine\n3647\n5\nk\nsun48\n3629\n6\nj\niangly\n3616\n7\nt\nurmax\n3559\n8\ns\ntrapple\n3486\n9\nd\nXqwq\n3436\n10\nK\nevin114514\n3427\n→ Top contributors\n#\nUser\nContrib.\n1\nQ\ningyu\n158\n2\nadamant\n153\n3\nU\nm_nik\n152\n4\nD\nominater069\n147\n5\nProof_by_QED\n145\n6\ne\nrrorgorn\n144\n7\ncry\n140\n8\nYuukiS\n135\n8\nTheScrasse\n135\n10\nawoo\n134\n→ Find user\n→ Recent actions\nszawinis\nBlog\nTeams\nSubmissions\nGroups\nContests\nszawinis's blog\nPicking the base and mod for string hashing is very important in decreasing the probability of hash collisions. How much are the guidelines affected by the problem itself? So far, I've read that the base should be larger than the alphabet, and the mod should be really large (but not overflow). But is there anything else?","attrs_markdown":"[![Codeforces](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/codeforces-sponsored-by-ton.png)](https:\/\/codeforces.com\/)\n\n[![In English](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/flags\/24\/gb.png)](https:\/\/codeforces.com\/blog\/entry\/52697?locale=en) [![По-русски](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/flags\/24\/ru.png)](https:\/\/codeforces.com\/blog\/entry\/52697?locale=ru)\n\n[Enter](https:\/\/codeforces.com\/enter?back=%2Fblog%2Fentry%2F52697) \\| [Register](https:\/\/codeforces.com\/register)\n\n- [Home](https:\/\/codeforces.com\/)\n- [Top](https:\/\/codeforces.com\/top)\n- [Catalog](https:\/\/codeforces.com\/catalog)\n- [Contests](https:\/\/codeforces.com\/contests)\n- [Gym](https:\/\/codeforces.com\/gyms)\n- [Problemset](https:\/\/codeforces.com\/problemset)\n- [Groups](https:\/\/codeforces.com\/groups)\n- [Rating](https:\/\/codeforces.com\/ratings)\n- [Edu](https:\/\/codeforces.com\/edu\/courses)\n- [API](https:\/\/codeforces.com\/apiHelp)\n- [Calendar](https:\/\/codeforces.com\/calendar)\n- [Help](https:\/\/codeforces.com\/help)\n\n→ Pay attention\n\nBefore contest  \n[Codeforces Round (Div. 2)](https:\/\/codeforces.com\/contests\/2217)  \n5 days  \n[Register now »](https:\/\/codeforces.com\/contestRegistration\/2217)\n\n\\*has extra registration\n\n→ Top rated\n\n| \\# | User | Rating |\n|---|---|---|\n| 1 | [Benq](https:\/\/codeforces.com\/profile\/Benq \"Legendary Grandmaster Benq\") | 3792 |\n| 2 | [tourist](https:\/\/codeforces.com\/profile\/tourist \"Legendary Grandmaster tourist\") | 3755 |\n| 3 | [ecnerwala](https:\/\/codeforces.com\/profile\/ecnerwala \"Legendary Grandmaster ecnerwala\") | 3696 |\n| 4 | [VivaciousAubergine](https:\/\/codeforces.com\/profile\/VivaciousAubergine \"Legendary Grandmaster VivaciousAubergine\") | 3647 |\n| 5 | [ksun48](https:\/\/codeforces.com\/profile\/ksun48 \"Legendary Grandmaster ksun48\") | 3629 |\n| 6 | [jiangly](https:\/\/codeforces.com\/profile\/jiangly \"Legendary Grandmaster jiangly\") | 3616 |\n| 7 | [turmax](https:\/\/codeforces.com\/profile\/turmax \"Legendary Grandmaster turmax\") | 3559 |\n| 8 | [strapple](https:\/\/codeforces.com\/profile\/strapple \"Legendary Grandmaster strapple\") | 3486 |\n| 9 | [dXqwq](https:\/\/codeforces.com\/profile\/dXqwq \"Legendary Grandmaster dXqwq\") | 3436 |\n| 10 | [Kevin114514](https:\/\/codeforces.com\/profile\/Kevin114514 \"Legendary Grandmaster Kevin114514\") | 3427 |\n\n|   |   |\n|---|---|\n| [Countries](https:\/\/codeforces.com\/ratings\/countries) \\| [Cities](https:\/\/codeforces.com\/ratings\/cities) \\| [Organizations](https:\/\/codeforces.com\/ratings\/organizations) | [View all →](https:\/\/codeforces.com\/ratings) |\n\n→ Top contributors\n\n| \\# | User | Contrib. |\n|---|---|---|\n| 1 | [Qingyu](https:\/\/codeforces.com\/profile\/Qingyu \"Legendary Grandmaster Qingyu\") | 158 |\n| 2 | [adamant](https:\/\/codeforces.com\/profile\/adamant \"Master adamant\") | 153 |\n| 3 | [Um\\_nik](https:\/\/codeforces.com\/profile\/Um_nik \"Legendary Grandmaster Um_nik\") | 152 |\n| 4 | [Dominater069](https:\/\/codeforces.com\/profile\/Dominater069 \"Legendary Grandmaster Dominater069\") | 147 |\n| 5 | [Proof\\_by\\_QED](https:\/\/codeforces.com\/profile\/Proof_by_QED \"International Master Proof_by_QED\") | 145 |\n| 6 | [errorgorn](https:\/\/codeforces.com\/profile\/errorgorn \"Legendary Grandmaster errorgorn\") | 144 |\n| 7 | [cry](https:\/\/codeforces.com\/profile\/cry \"International Master cry\") | 140 |\n| 8 | [YuukiS](https:\/\/codeforces.com\/profile\/YuukiS \"International Grandmaster YuukiS\") | 135 |\n| 8 | [TheScrasse](https:\/\/codeforces.com\/profile\/TheScrasse \"Grandmaster TheScrasse\") | 135 |\n| 10 | [awoo](https:\/\/codeforces.com\/profile\/awoo \"Grandmaster awoo\") | 134 |\n\n|   |   |\n|---|---|\n|   | [View all →](https:\/\/codeforces.com\/top-contributed) |\n\n→ Find user\n\n→ Recent actions\n\n- [Um\\_nik](https:\/\/codeforces.com\/profile\/Um_nik \"Legendary Grandmaster Um_nik\") → [How to read problem statements](https:\/\/codeforces.com\/blog\/entry\/62730) ![New comment(s)](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/icons\/comment-12x12.png) ![Necropost](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/icons\/hourglass.png)\n- [nifeshe](https:\/\/codeforces.com\/profile\/nifeshe \"Grandmaster nifeshe\") → [Codeforces Round 997 (Div. 2)](https:\/\/codeforces.com\/blog\/entry\/138420) ![New comment(s)](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/icons\/comment-12x12.png) ![Necropost](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/icons\/hourglass.png)\n- [joelgun14](https:\/\/codeforces.com\/profile\/joelgun14 \"Master joelgun14\") → [The ICPC NAC 2026 Experience](https:\/\/codeforces.com\/blog\/entry\/152257) ![New comment(s)](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/icons\/comment-12x12.png)\n- [Argentum47](https:\/\/codeforces.com\/profile\/Argentum47 \"Expert Argentum47\") → [Codeforces Round 1089 (Div. 2)](https:\/\/codeforces.com\/blog\/entry\/152376) ![New comment(s)](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/icons\/comment-12x12.png)\n- [m7a1g5i8k8a1r4p0](https:\/\/codeforces.com\/profile\/m7a1g5i8k8a1r4p0 \"Master m7a1g5i8k8a1r4p0\") → [UTPC April Fool's Contest 2026 Editorial](https:\/\/codeforces.com\/blog\/entry\/152595) ![New comment(s)](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/icons\/comment-12x12.png)\n- [programmercat](https:\/\/codeforces.com\/profile\/programmercat \"Specialist programmercat\") → [Happy Autism Awareness Day](https:\/\/codeforces.com\/blog\/entry\/152598)  ![New comment(s)](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/icons\/comment-12x12.png)\n- [jerrywang0916](https:\/\/codeforces.com\/profile\/jerrywang0916 \"Expert jerrywang0916\") → [List of Suspected Cheaters in Nebius Round 2](https:\/\/codeforces.com\/blog\/entry\/152532) ![New comment(s)](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/icons\/comment-12x12.png)\n- [ToxicPie9](https:\/\/codeforces.com\/profile\/ToxicPie9 \"Candidate Master ToxicPie9\") → [April Fools Day Contest 2026 Editorial](https:\/\/codeforces.com\/blog\/entry\/152573) ![Text created or updated](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/icons\/x-update-12x12.png)\n- [CarViz](https:\/\/codeforces.com\/profile\/CarViz \"Expert CarViz\") → [fraud in the philipines\\!](https:\/\/codeforces.com\/blog\/entry\/152594) ![Text created or updated](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/icons\/x-update-12x12.png)\n- [AlperenT](https:\/\/codeforces.com\/profile\/AlperenT \"Master AlperenT\") → [April Fools Day Contest 2026](https:\/\/codeforces.com\/blog\/entry\/152445) ![New comment(s)](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/icons\/comment-12x12.png)\n- [AlexandruINV](https:\/\/codeforces.com\/profile\/AlexandruINV \"Expert AlexandruINV\") → [A Friendly Competitive Programming Discord Server\\!](https:\/\/codeforces.com\/blog\/entry\/151914) ![Text created or updated](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/icons\/x-update-12x12.png)\n- [macaquedev](https:\/\/codeforces.com\/profile\/macaquedev \"Candidate Master macaquedev\") → [April Fools Day Contest 2026 Definitely Official Editorial](https:\/\/codeforces.com\/blog\/entry\/152580)  ![New comment(s)](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/icons\/comment-12x12.png)\n- [abhinav4710](https:\/\/codeforces.com\/profile\/abhinav4710 \"Expert abhinav4710\") → [Issues with the latest plagiarism check issued](https:\/\/codeforces.com\/blog\/entry\/152589) ![New comment(s)](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/icons\/comment-12x12.png)\n- [\\_\\_AB\\_\\_](https:\/\/codeforces.com\/profile\/__AB__ \"Expert __AB__\") → [High Expectations from Expectations](https:\/\/codeforces.com\/blog\/entry\/152586) ![New comment(s)](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/icons\/comment-12x12.png)\n- [uranaitnazarov](https:\/\/codeforces.com\/profile\/uranaitnazarov \"Newbie uranaitnazarov\") → [why would yall dislike my comment its peak bruh \\#haters dawg](https:\/\/codeforces.com\/blog\/entry\/152596) ![Text created or updated](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/icons\/x-update-12x12.png)\n- [hasan2](https:\/\/codeforces.com\/profile\/hasan2 \"Newbie hasan2\") → [HASAN](https:\/\/codeforces.com\/blog\/entry\/152584) ![New comment(s)](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/icons\/comment-12x12.png)\n- [holl0w](https:\/\/codeforces.com\/profile\/holl0w \"Master holl0w\") → [FlandeOJ, yet another competitive programming roadmap...](https:\/\/codeforces.com\/blog\/entry\/152552) ![New comment(s)](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/icons\/comment-12x12.png)\n- [macaquedev](https:\/\/codeforces.com\/profile\/macaquedev \"Candidate Master macaquedev\") → [Blatant Thievery](https:\/\/codeforces.com\/blog\/entry\/152588) ![New comment(s)](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/icons\/comment-12x12.png)\n- [yanb0](https:\/\/codeforces.com\/profile\/yanb0 \"Master yanb0\") → [Codeforces Round 1075 (Div. 2) Editorial](https:\/\/codeforces.com\/blog\/entry\/150452) ![New comment(s)](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/icons\/comment-12x12.png)\n- [Ritwin](https:\/\/codeforces.com\/profile\/Ritwin \"Master Ritwin\") → [Stanford Local Programming Contest 2026](https:\/\/codeforces.com\/blog\/entry\/152392) ![New comment(s)](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/icons\/comment-12x12.png)\n- [krakar](https:\/\/codeforces.com\/profile\/krakar \"Expert krakar\") → [Falsely Suspected of Cheating](https:\/\/codeforces.com\/blog\/entry\/152590)  ![Text created or updated](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/icons\/x-update-12x12.png)\n- [tinyfold](https:\/\/codeforces.com\/profile\/tinyfold \"Expert tinyfold\") → [Guys I have a CONFESSION](https:\/\/codeforces.com\/blog\/entry\/152562) ![New comment(s)](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/icons\/comment-12x12.png)\n- [Saad\\_aa](https:\/\/codeforces.com\/profile\/Saad_aa \"Newbie Saad_aa\") → [Help needed For a more optimal solution](https:\/\/codeforces.com\/blog\/entry\/152583) ![New comment(s)](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/icons\/comment-12x12.png)\n- [MikeMirzayanov](https:\/\/codeforces.com\/profile\/MikeMirzayanov \"Headquarters, MikeMirzayanov\") → [Rule about third-party code is changing](https:\/\/codeforces.com\/blog\/entry\/8790) ![New comment(s)](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/icons\/comment-12x12.png) ![Necropost](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/icons\/hourglass.png)\n- [Anadi](https:\/\/codeforces.com\/profile\/Anadi \"International Grandmaster Anadi\") → [Codeforces Round \\#519 Editorial](https:\/\/codeforces.com\/blog\/entry\/62797) ![New comment(s)](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/icons\/comment-12x12.png) ![Necropost](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/icons\/hourglass.png)\n\n|   |   |\n|---|---|\n|   | [Detailed →](https:\/\/codeforces.com\/recent-actions) |\n\n- [szawinis](https:\/\/codeforces.com\/profile\/szawinis)\n- [Blog](https:\/\/codeforces.com\/blog\/szawinis)\n- [Teams](https:\/\/codeforces.com\/teams\/with\/szawinis)\n- [Submissions](https:\/\/codeforces.com\/submissions\/szawinis)\n- [Groups](https:\/\/codeforces.com\/groups\/with\/szawinis)\n- [Contests](https:\/\/codeforces.com\/contests\/with\/szawinis)\n\n### [szawinis's blog](https:\/\/codeforces.com\/blog\/szawinis)\n[Hashing: How to pick base and mod?](https:\/\/codeforces.com\/blog\/entry\/52697)\n\nBy [szawinis](https:\/\/codeforces.com\/profile\/szawinis \"Candidate Master szawinis\"), [history](https:\/\/codeforces.com\/topic\/52953\/en1), 9 years ago, ![In English](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/flags\/24\/gb.png)\n\nPicking the base and mod for string hashing is very important in decreasing the probability of hash collisions. How much are the guidelines affected by the problem itself? So far, I've read that the base should be larger than the alphabet, and the mod should be really large (but not overflow). But is there anything else?\n\n- [![Vote: I like it](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/actions\/voteup-gray.png)](https:\/\/codeforces.com\/blog\/entry\/52697)\n- \\+14\n- [![Vote: I do not like it](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/actions\/votedown-gray.png)](https:\/\/codeforces.com\/blog\/entry\/52697)\n\n- [![Author](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/blog\/user_16x16.png)](https:\/\/codeforces.com\/profile\/szawinis)  [szawinis](https:\/\/codeforces.com\/profile\/szawinis)\n- ![Publication date](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/blog\/date_16x16.png) 9 years ago\n- [![Comments](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/blog\/comments_16x16.png)](https:\/\/codeforces.com\/blog\/entry\/52697#comments)  [5](https:\/\/codeforces.com\/blog\/entry\/52697#comments)\n\n![Comments](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/icons\/comments-48x48.png) [Comments (4)]()\n\nShow archived\n\n\\| [Write comment?](https:\/\/codeforces.com\/blog\/entry\/52697)\n\n|   |   |\n|---|---|\n| » [gongy](https:\/\/codeforces.com\/profile\/gongy \"Grandmaster gongy\") | 9 years ago, [show (+1)](https:\/\/codeforces.com\/blog\/entry\/52697) [\\#]() |\n\n|   |   |\n|---|---|\n| » [![](https:\/\/codeforces.com\/userpic.codeforces.org\/221466\/avatar\/76e12a6a59ea145.jpg)](https:\/\/codeforces.com\/profile\/gongy) [gongy](https:\/\/codeforces.com\/profile\/gongy \"Grandmaster gongy\") | 9 years ago, [hide](https:\/\/codeforces.com\/blog\/entry\/52697) [\\#](https:\/\/codeforces.com\/blog\/entry\/52697#comment-367252 \"Link to comment\") \\| [![Vote: I like it](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/actions\/comment-voteup-blue.png)](https:\/\/codeforces.com\/blog\/entry\/52697) \\+18 [![Vote: I do not like it](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/actions\/comment-votedown-blue.png)](https:\/\/codeforces.com\/blog\/entry\/52697) You sound like you are on the right track. The base and mod must be coprime — usually, you just choose a prime base and prime mod anyway. Furthermore, you usually need hash two or more mods to stay safe. This is because of the birthday paradox. Normally people use base 137 and hash in 1e9+7 and 1e9+9. [→](https:\/\/codeforces.com\/blog\/entry\/52697) [Reply](https:\/\/codeforces.com\/blog\/entry\/52697) |\n\n- |   |   |\n  |---|---|\n  | » » [yeputons](https:\/\/codeforces.com\/profile\/yeputons \"Grandmaster yeputons\") | 9 years ago, [show](https:\/\/codeforces.com\/blog\/entry\/52697) [\\#]() |\n  \n  |   |   |\n  |---|---|\n  | » » [![](https:\/\/codeforces.com\/userpic.codeforces.org\/2412\/avatar\/cfc26825136c163e.jpg)](https:\/\/codeforces.com\/profile\/yeputons) [yeputons](https:\/\/codeforces.com\/profile\/yeputons \"Grandmaster yeputons\") | 9 years ago, [hide](https:\/\/codeforces.com\/blog\/entry\/52697) [\\#](https:\/\/codeforces.com\/blog\/entry\/52697#comment-367302 \"Link to comment\") [^](https:\/\/codeforces.com\/blog\/entry\/52697#comment-367252 \"Parent comment\") \\| [![Vote: I like it](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/actions\/comment-voteup-blue.png)](https:\/\/codeforces.com\/blog\/entry\/52697) \\+13 [![Vote: I do not like it](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/actions\/comment-votedown-blue.png)](https:\/\/codeforces.com\/blog\/entry\/52697) Base should also be strictly greater than the number of different values an individual element can be. E.g. 137 is enough for English latters, but not enough for arbitrary `char`s. Also, it's good to ensure that all codes of individual elements are between 0 and `base-1` so they do not collide modulo `base` for some random reason. [→](https:\/\/codeforces.com\/blog\/entry\/52697) [Reply](https:\/\/codeforces.com\/blog\/entry\/52697) |\n- |   |   |\n  |---|---|\n  | » » [\\_Dormammu\\_](https:\/\/codeforces.com\/profile\/_Dormammu_ \"Expert _Dormammu_\") | 6 years ago, [show](https:\/\/codeforces.com\/blog\/entry\/52697) [\\#]() |\n  \n  |   |   |\n  |---|---|\n  | » » [![](https:\/\/codeforces.com\/userpic.codeforces.org\/925391\/avatar\/48e3328b21fdb3b0.jpg)](https:\/\/codeforces.com\/profile\/_Dormammu_) [\\_Dormammu\\_](https:\/\/codeforces.com\/profile\/_Dormammu_ \"Expert _Dormammu_\") | 6 years ago, [hide](https:\/\/codeforces.com\/blog\/entry\/52697) [\\#](https:\/\/codeforces.com\/blog\/entry\/52697#comment-589514 \"Link to comment\") [^](https:\/\/codeforces.com\/blog\/entry\/52697#comment-367252 \"Parent comment\") \\| [←](https:\/\/codeforces.com\/blog\/entry\/52697) Rev. 2 [→](https:\/\/codeforces.com\/blog\/entry\/52697) [![Vote: I like it](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/actions\/comment-voteup-blue.png)](https:\/\/codeforces.com\/blog\/entry\/52697) \\-24 [![Vote: I do not like it](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/actions\/comment-votedown-blue.png)](https:\/\/codeforces.com\/blog\/entry\/52697) :) [→](https:\/\/codeforces.com\/blog\/entry\/52697) [Reply](https:\/\/codeforces.com\/blog\/entry\/52697) |\n\n|   |   |\n|---|---|\n| » [bhishma](https:\/\/codeforces.com\/profile\/bhishma \"Expert bhishma\") | 9 years ago, [show](https:\/\/codeforces.com\/blog\/entry\/52697) [\\#]() |\n\n|   |   |\n|---|---|\n| » [![](https:\/\/codeforces.com\/userpic.codeforces.org\/305276\/avatar\/83814e515ace8f09.jpg)](https:\/\/codeforces.com\/profile\/bhishma) [bhishma](https:\/\/codeforces.com\/profile\/bhishma \"Expert bhishma\") | 9 years ago, [hide](https:\/\/codeforces.com\/blog\/entry\/52697) [\\#](https:\/\/codeforces.com\/blog\/entry\/52697#comment-367357 \"Link to comment\") \\| [![Vote: I like it](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/actions\/comment-voteup-blue.png)](https:\/\/codeforces.com\/blog\/entry\/52697) \\+21 [![Vote: I do not like it](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/actions\/comment-votedown-blue.png)](https:\/\/codeforces.com\/blog\/entry\/52697) This topics has been discussed a lot of times. [Where to Use and How not to Use Polynomial String Hashing (PACHOCK,RADOSZEWSKI)](https:\/\/www.mii.lt\/olympiads_in_informatics\/pdf\/INFOL119.pdf) [Anti-hash test](https:\/\/codeforces.com\/blog\/entry\/4898) [→](https:\/\/codeforces.com\/blog\/entry\/52697) [Reply](https:\/\/codeforces.com\/blog\/entry\/52697) |\n\nIn English\n\nIn Russian\n\n↑\n***\n\n***\n↓\n\n[Codeforces](https:\/\/codeforces.com\/) (c) Copyright 2010-2026 Mike Mirzayanov\n\nThe only programming contests Web 2.0 platform\n\nServer time: Apr\/02\/2026 09:45:09 (l2).\n\nDesktop version, switch to [mobile version](https:\/\/codeforces.com\/blog\/entry\/52697?mobile=true).\n\n[Privacy Policy](https:\/\/codeforces.com\/privacy) \\| [Terms and Conditions](https:\/\/codeforces.com\/terms)\n\nSupported by\n\n[![TON](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/ton-100x100.png)](https:\/\/ton.org\/)\n\nUser lists\n\n![](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/icons\/magnifier-medium.png)\n\n![](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/icons\/control-270.png)\n\n| Name |\n|---|","attrs_readable_markdown":"[![Codeforces](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/codeforces-sponsored-by-ton.png)](https:\/\/codeforces.com\/)\n\n[![In English](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/flags\/24\/gb.png)](https:\/\/codeforces.com\/blog\/entry\/52697?locale=en) [![По-русски](https:\/\/codeforces.com\/codeforces.org\/s\/87877\/images\/flags\/24\/ru.png)](https:\/\/codeforces.com\/blog\/entry\/52697?locale=ru)\n\n→ Pay attention\n\n→ Top rated\n\n| \\# | User | Rating |\n|---|---|---|\n| 1 | [Benq](https:\/\/codeforces.com\/profile\/Benq \"Legendary Grandmaster Benq\") | 3792 |\n| 2 | [tourist](https:\/\/codeforces.com\/profile\/tourist \"Legendary Grandmaster tourist\") | 3755 |\n| 3 | [ecnerwala](https:\/\/codeforces.com\/profile\/ecnerwala \"Legendary Grandmaster ecnerwala\") | 3696 |\n| 4 | [VivaciousAubergine](https:\/\/codeforces.com\/profile\/VivaciousAubergine \"Legendary Grandmaster VivaciousAubergine\") | 3647 |\n| 5 | [ksun48](https:\/\/codeforces.com\/profile\/ksun48 \"Legendary Grandmaster ksun48\") | 3629 |\n| 6 | [jiangly](https:\/\/codeforces.com\/profile\/jiangly \"Legendary Grandmaster jiangly\") | 3616 |\n| 7 | [turmax](https:\/\/codeforces.com\/profile\/turmax \"Legendary Grandmaster turmax\") | 3559 |\n| 8 | [strapple](https:\/\/codeforces.com\/profile\/strapple \"Legendary Grandmaster strapple\") | 3486 |\n| 9 | [dXqwq](https:\/\/codeforces.com\/profile\/dXqwq \"Legendary Grandmaster dXqwq\") | 3436 |\n| 10 | [Kevin114514](https:\/\/codeforces.com\/profile\/Kevin114514 \"Legendary Grandmaster Kevin114514\") | 3427 |\n\n→ Top contributors\n\n| \\# | User | Contrib. |\n|---|---|---|\n| 1 | [Qingyu](https:\/\/codeforces.com\/profile\/Qingyu \"Legendary Grandmaster Qingyu\") | 158 |\n| 2 | [adamant](https:\/\/codeforces.com\/profile\/adamant \"Master adamant\") | 153 |\n| 3 | [Um\\_nik](https:\/\/codeforces.com\/profile\/Um_nik \"Legendary Grandmaster Um_nik\") | 152 |\n| 4 | [Dominater069](https:\/\/codeforces.com\/profile\/Dominater069 \"Legendary Grandmaster Dominater069\") | 147 |\n| 5 | [Proof\\_by\\_QED](https:\/\/codeforces.com\/profile\/Proof_by_QED \"International Master Proof_by_QED\") | 145 |\n| 6 | [errorgorn](https:\/\/codeforces.com\/profile\/errorgorn \"Legendary Grandmaster errorgorn\") | 144 |\n| 7 | [cry](https:\/\/codeforces.com\/profile\/cry \"International Master cry\") | 140 |\n| 8 | [YuukiS](https:\/\/codeforces.com\/profile\/YuukiS \"International Grandmaster YuukiS\") | 135 |\n| 8 | [TheScrasse](https:\/\/codeforces.com\/profile\/TheScrasse \"Grandmaster TheScrasse\") | 135 |\n| 10 | [awoo](https:\/\/codeforces.com\/profile\/awoo \"Grandmaster awoo\") | 134 |\n\n→ Find user\n\n→ Recent actions\n\n- [szawinis](https:\/\/codeforces.com\/profile\/szawinis)\n- [Blog](https:\/\/codeforces.com\/blog\/szawinis)\n- [Teams](https:\/\/codeforces.com\/teams\/with\/szawinis)\n- [Submissions](https:\/\/codeforces.com\/submissions\/szawinis)\n- [Groups](https:\/\/codeforces.com\/groups\/with\/szawinis)\n- [Contests](https:\/\/codeforces.com\/contests\/with\/szawinis)\n\n[szawinis's blog](https:\/\/codeforces.com\/blog\/szawinis)\n\nPicking the base and mod for string hashing is very important in decreasing the probability of hash collisions. How much are the guidelines affected by the problem itself? So far, I've read that the base should be larger than the alphabet, and the mod should be really large (but not overflow). But is there anything else?","meta_canonical":null}

3. Robots.txt Check

Query:

Response:

4. Spam/Ban Check

Query:

Response:

5. Seen Status Check

ℹ️ Skipped - page is already crawled

📄

INDEXABLE

✅

CRAWLED

14 days ago

🤖

ROBOTS ALLOWED

Page Info Filters

Filter	Status	Condition	Details
HTTP status	PASS	`download_http_code = 200`	HTTP 200
Age cutoff	PASS	`download_stamp > now() - 6 MONTH`	0.5 months ago
History drop	PASS	`isNull(history_drop_reason)`	No drop reason
Spam/ban	PASS	`fh_dont_index != 1 AND ml_spam_score = 0`	ml_spam_score=0
Canonical	PASS	`meta_canonical IS NULL OR = '' OR = src_unparsed`	Not set

Page Details

Property	Value
URL	https://codeforces.com/blog/entry/52697
Last Crawled	2026-04-02 06:45:09 (14 days ago)
First Indexed	2018-12-19 21:53:19 (7 years ago)
HTTP Status Code	200
Meta Title	Hashing: How to pick base and mod? - Codeforces
Meta Description	Codeforces. Programming competitions and contests, programming community
Meta Canonical	null
Boilerpipe Text	→ Pay attention → Top rated # User Rating 1 B enq 3792 2 t ourist 3755 3 e cnerwala 3696 4 V ivaciousAubergine 3647 5 k sun48 3629 6 j iangly 3616 7 t urmax 3559 8 s trapple 3486 9 d Xqwq 3436 10 K evin114514 3427 → Top contributors # User Contrib. 1 Q ingyu 158 2 adamant 153 3 U m_nik 152 4 D ominater069 147 5 Proof_by_QED 145 6 e rrorgorn 144 7 cry 140 8 YuukiS 135 8 TheScrasse 135 10 awoo 134 → Find user → Recent actions szawinis Blog Teams Submissions Groups Contests szawinis's blog Picking the base and mod for string hashing is very important in decreasing the probability of hash collisions. How much are the guidelines affected by the problem itself? So far, I've read that the base should be larger than the alphabet, and the mod should be really large (but not overflow). But is there anything else?
Markdown	[![Codeforces](https://codeforces.com/codeforces.org/s/87877/images/codeforces-sponsored-by-ton.png)](https://codeforces.com/) [![In English](https://codeforces.com/codeforces.org/s/87877/images/flags/24/gb.png)](https://codeforces.com/blog/entry/52697?locale=en) [![По-русски](https://codeforces.com/codeforces.org/s/87877/images/flags/24/ru.png)](https://codeforces.com/blog/entry/52697?locale=ru) [Enter](https://codeforces.com/enter?back=%2Fblog%2Fentry%2F52697) \\| [Register](https://codeforces.com/register) - [Home](https://codeforces.com/) - [Top](https://codeforces.com/top) - [Catalog](https://codeforces.com/catalog) - [Contests](https://codeforces.com/contests) - [Gym](https://codeforces.com/gyms) - [Problemset](https://codeforces.com/problemset) - [Groups](https://codeforces.com/groups) - [Rating](https://codeforces.com/ratings) - [Edu](https://codeforces.com/edu/courses) - [API](https://codeforces.com/apiHelp) - [Calendar](https://codeforces.com/calendar) - [Help](https://codeforces.com/help) → Pay attention Before contest [Codeforces Round (Div. 2)](https://codeforces.com/contests/2217) 5 days [Register now »](https://codeforces.com/contestRegistration/2217) \has extra registration → Top rated \| \# \| User \| Rating \| \|---\|---\|---\| \| 1 \| [Benq](https://codeforces.com/profile/Benq "Legendary Grandmaster Benq") \| 3792 \| \| 2 \| [tourist](https://codeforces.com/profile/tourist "Legendary Grandmaster tourist") \| 3755 \| \| 3 \| [ecnerwala](https://codeforces.com/profile/ecnerwala "Legendary Grandmaster ecnerwala") \| 3696 \| \| 4 \| [VivaciousAubergine](https://codeforces.com/profile/VivaciousAubergine "Legendary Grandmaster VivaciousAubergine") \| 3647 \| \| 5 \| [ksun48](https://codeforces.com/profile/ksun48 "Legendary Grandmaster ksun48") \| 3629 \| \| 6 \| [jiangly](https://codeforces.com/profile/jiangly "Legendary Grandmaster jiangly") \| 3616 \| \| 7 \| [turmax](https://codeforces.com/profile/turmax "Legendary Grandmaster turmax") \| 3559 \| \| 8 \| [strapple](https://codeforces.com/profile/strapple "Legendary Grandmaster strapple") \| 3486 \| \| 9 \| [dXqwq](https://codeforces.com/profile/dXqwq "Legendary Grandmaster dXqwq") \| 3436 \| \| 10 \| [Kevin114514](https://codeforces.com/profile/Kevin114514 "Legendary Grandmaster Kevin114514") \| 3427 \| \| \| \| \|---\|---\| \| [Countries](https://codeforces.com/ratings/countries) \\| [Cities](https://codeforces.com/ratings/cities) \\| [Organizations](https://codeforces.com/ratings/organizations) \| [View all →](https://codeforces.com/ratings) \| → Top contributors \| \# \| User \| Contrib. \| \|---\|---\|---\| \| 1 \| [Qingyu](https://codeforces.com/profile/Qingyu "Legendary Grandmaster Qingyu") \| 158 \| \| 2 \| [adamant](https://codeforces.com/profile/adamant "Master adamant") \| 153 \| \| 3 \| [Um\_nik](https://codeforces.com/profile/Um_nik "Legendary Grandmaster Um_nik") \| 152 \| \| 4 \| [Dominater069](https://codeforces.com/profile/Dominater069 "Legendary Grandmaster Dominater069") \| 147 \| \| 5 \| [Proof\_by\_QED](https://codeforces.com/profile/Proof_by_QED "International Master Proof_by_QED") \| 145 \| \| 6 \| [errorgorn](https://codeforces.com/profile/errorgorn "Legendary Grandmaster errorgorn") \| 144 \| \| 7 \| [cry](https://codeforces.com/profile/cry "International Master cry") \| 140 \| \| 8 \| [YuukiS](https://codeforces.com/profile/YuukiS "International Grandmaster YuukiS") \| 135 \| \| 8 \| [TheScrasse](https://codeforces.com/profile/TheScrasse "Grandmaster TheScrasse") \| 135 \| \| 10 \| [awoo](https://codeforces.com/profile/awoo "Grandmaster awoo") \| 134 \| \| \| \| \|---\|---\| \| \| [View all →](https://codeforces.com/top-contributed) \| → Find user → Recent actions - [Um\_nik](https://codeforces.com/profile/Um_nik "Legendary Grandmaster Um_nik") → [How to read problem statements](https://codeforces.com/blog/entry/62730) ![New comment(s)](https://codeforces.com/codeforces.org/s/87877/images/icons/comment-12x12.png) ![Necropost](https://codeforces.com/codeforces.org/s/87877/images/icons/hourglass.png) - [nifeshe](https://codeforces.com/profile/nifeshe "Grandmaster nifeshe") → [Codeforces Round 997 (Div. 2)](https://codeforces.com/blog/entry/138420) ![New comment(s)](https://codeforces.com/codeforces.org/s/87877/images/icons/comment-12x12.png) ![Necropost](https://codeforces.com/codeforces.org/s/87877/images/icons/hourglass.png) - [joelgun14](https://codeforces.com/profile/joelgun14 "Master joelgun14") → [The ICPC NAC 2026 Experience](https://codeforces.com/blog/entry/152257) ![New comment(s)](https://codeforces.com/codeforces.org/s/87877/images/icons/comment-12x12.png) - [Argentum47](https://codeforces.com/profile/Argentum47 "Expert Argentum47") → [Codeforces Round 1089 (Div. 2)](https://codeforces.com/blog/entry/152376) ![New comment(s)](https://codeforces.com/codeforces.org/s/87877/images/icons/comment-12x12.png) - [m7a1g5i8k8a1r4p0](https://codeforces.com/profile/m7a1g5i8k8a1r4p0 "Master m7a1g5i8k8a1r4p0") → [UTPC April Fool's Contest 2026 Editorial](https://codeforces.com/blog/entry/152595) ![New comment(s)](https://codeforces.com/codeforces.org/s/87877/images/icons/comment-12x12.png) - [programmercat](https://codeforces.com/profile/programmercat "Specialist programmercat") → [Happy Autism Awareness Day](https://codeforces.com/blog/entry/152598) ![New comment(s)](https://codeforces.com/codeforces.org/s/87877/images/icons/comment-12x12.png) - [jerrywang0916](https://codeforces.com/profile/jerrywang0916 "Expert jerrywang0916") → [List of Suspected Cheaters in Nebius Round 2](https://codeforces.com/blog/entry/152532) ![New comment(s)](https://codeforces.com/codeforces.org/s/87877/images/icons/comment-12x12.png) - [ToxicPie9](https://codeforces.com/profile/ToxicPie9 "Candidate Master ToxicPie9") → [April Fools Day Contest 2026 Editorial](https://codeforces.com/blog/entry/152573) ![Text created or updated](https://codeforces.com/codeforces.org/s/87877/images/icons/x-update-12x12.png) - [CarViz](https://codeforces.com/profile/CarViz "Expert CarViz") → [fraud in the philipines\!](https://codeforces.com/blog/entry/152594) ![Text created or updated](https://codeforces.com/codeforces.org/s/87877/images/icons/x-update-12x12.png) - [AlperenT](https://codeforces.com/profile/AlperenT "Master AlperenT") → [April Fools Day Contest 2026](https://codeforces.com/blog/entry/152445) ![New comment(s)](https://codeforces.com/codeforces.org/s/87877/images/icons/comment-12x12.png) - [AlexandruINV](https://codeforces.com/profile/AlexandruINV "Expert AlexandruINV") → [A Friendly Competitive Programming Discord Server\!](https://codeforces.com/blog/entry/151914) ![Text created or updated](https://codeforces.com/codeforces.org/s/87877/images/icons/x-update-12x12.png) - [macaquedev](https://codeforces.com/profile/macaquedev "Candidate Master macaquedev") → [April Fools Day Contest 2026 Definitely Official Editorial](https://codeforces.com/blog/entry/152580) ![New comment(s)](https://codeforces.com/codeforces.org/s/87877/images/icons/comment-12x12.png) - [abhinav4710](https://codeforces.com/profile/abhinav4710 "Expert abhinav4710") → [Issues with the latest plagiarism check issued](https://codeforces.com/blog/entry/152589) ![New comment(s)](https://codeforces.com/codeforces.org/s/87877/images/icons/comment-12x12.png) - [\_\_AB\_\_](https://codeforces.com/profile/__AB__ "Expert __AB__") → [High Expectations from Expectations](https://codeforces.com/blog/entry/152586) ![New comment(s)](https://codeforces.com/codeforces.org/s/87877/images/icons/comment-12x12.png) - [uranaitnazarov](https://codeforces.com/profile/uranaitnazarov "Newbie uranaitnazarov") → [why would yall dislike my comment its peak bruh \#haters dawg](https://codeforces.com/blog/entry/152596) ![Text created or updated](https://codeforces.com/codeforces.org/s/87877/images/icons/x-update-12x12.png) - [hasan2](https://codeforces.com/profile/hasan2 "Newbie hasan2") → [HASAN](https://codeforces.com/blog/entry/152584) ![New comment(s)](https://codeforces.com/codeforces.org/s/87877/images/icons/comment-12x12.png) - [holl0w](https://codeforces.com/profile/holl0w "Master holl0w") → [FlandeOJ, yet another competitive programming roadmap...](https://codeforces.com/blog/entry/152552) ![New comment(s)](https://codeforces.com/codeforces.org/s/87877/images/icons/comment-12x12.png) - [macaquedev](https://codeforces.com/profile/macaquedev "Candidate Master macaquedev") → [Blatant Thievery](https://codeforces.com/blog/entry/152588) ![New comment(s)](https://codeforces.com/codeforces.org/s/87877/images/icons/comment-12x12.png) - [yanb0](https://codeforces.com/profile/yanb0 "Master yanb0") → [Codeforces Round 1075 (Div. 2) Editorial](https://codeforces.com/blog/entry/150452) ![New comment(s)](https://codeforces.com/codeforces.org/s/87877/images/icons/comment-12x12.png) - [Ritwin](https://codeforces.com/profile/Ritwin "Master Ritwin") → [Stanford Local Programming Contest 2026](https://codeforces.com/blog/entry/152392) ![New comment(s)](https://codeforces.com/codeforces.org/s/87877/images/icons/comment-12x12.png) - [krakar](https://codeforces.com/profile/krakar "Expert krakar") → [Falsely Suspected of Cheating](https://codeforces.com/blog/entry/152590) ![Text created or updated](https://codeforces.com/codeforces.org/s/87877/images/icons/x-update-12x12.png) - [tinyfold](https://codeforces.com/profile/tinyfold "Expert tinyfold") → [Guys I have a CONFESSION](https://codeforces.com/blog/entry/152562) ![New comment(s)](https://codeforces.com/codeforces.org/s/87877/images/icons/comment-12x12.png) - [Saad\_aa](https://codeforces.com/profile/Saad_aa "Newbie Saad_aa") → [Help needed For a more optimal solution](https://codeforces.com/blog/entry/152583) ![New comment(s)](https://codeforces.com/codeforces.org/s/87877/images/icons/comment-12x12.png) - [MikeMirzayanov](https://codeforces.com/profile/MikeMirzayanov "Headquarters, MikeMirzayanov") → [Rule about third-party code is changing](https://codeforces.com/blog/entry/8790) ![New comment(s)](https://codeforces.com/codeforces.org/s/87877/images/icons/comment-12x12.png) ![Necropost](https://codeforces.com/codeforces.org/s/87877/images/icons/hourglass.png) - [Anadi](https://codeforces.com/profile/Anadi "International Grandmaster Anadi") → [Codeforces Round \#519 Editorial](https://codeforces.com/blog/entry/62797) ![New comment(s)](https://codeforces.com/codeforces.org/s/87877/images/icons/comment-12x12.png) ![Necropost](https://codeforces.com/codeforces.org/s/87877/images/icons/hourglass.png) \| \| \| \|---\|---\| \| \| [Detailed →](https://codeforces.com/recent-actions) \| - [szawinis](https://codeforces.com/profile/szawinis) - [Blog](https://codeforces.com/blog/szawinis) - [Teams](https://codeforces.com/teams/with/szawinis) - [Submissions](https://codeforces.com/submissions/szawinis) - [Groups](https://codeforces.com/groups/with/szawinis) - [Contests](https://codeforces.com/contests/with/szawinis) ### [szawinis's blog](https://codeforces.com/blog/szawinis) [Hashing: How to pick base and mod?](https://codeforces.com/blog/entry/52697) By [szawinis](https://codeforces.com/profile/szawinis "Candidate Master szawinis"), [history](https://codeforces.com/topic/52953/en1), 9 years ago, ![In English](https://codeforces.com/codeforces.org/s/87877/images/flags/24/gb.png) Picking the base and mod for string hashing is very important in decreasing the probability of hash collisions. How much are the guidelines affected by the problem itself? So far, I've read that the base should be larger than the alphabet, and the mod should be really large (but not overflow). But is there anything else? - [![Vote: I like it](https://codeforces.com/codeforces.org/s/87877/images/actions/voteup-gray.png)](https://codeforces.com/blog/entry/52697) - \+14 - [![Vote: I do not like it](https://codeforces.com/codeforces.org/s/87877/images/actions/votedown-gray.png)](https://codeforces.com/blog/entry/52697) - [![Author](https://codeforces.com/codeforces.org/s/87877/images/blog/user_16x16.png)](https://codeforces.com/profile/szawinis) [szawinis](https://codeforces.com/profile/szawinis) - ![Publication date](https://codeforces.com/codeforces.org/s/87877/images/blog/date_16x16.png) 9 years ago - [![Comments](https://codeforces.com/codeforces.org/s/87877/images/blog/comments_16x16.png)](https://codeforces.com/blog/entry/52697#comments) [5](https://codeforces.com/blog/entry/52697#comments) ![Comments](https://codeforces.com/codeforces.org/s/87877/images/icons/comments-48x48.png) [Comments (4)]() Show archived \\| [Write comment?](https://codeforces.com/blog/entry/52697) \| \| \| \|---\|---\| \| » [gongy](https://codeforces.com/profile/gongy "Grandmaster gongy") \| 9 years ago, [show (+1)](https://codeforces.com/blog/entry/52697) [\#]() \| \| \| \| \|---\|---\| \| » [![](https://codeforces.com/userpic.codeforces.org/221466/avatar/76e12a6a59ea145.jpg)](https://codeforces.com/profile/gongy) [gongy](https://codeforces.com/profile/gongy "Grandmaster gongy") \| 9 years ago, [hide](https://codeforces.com/blog/entry/52697) [\#](https://codeforces.com/blog/entry/52697#comment-367252 "Link to comment") \\| [![Vote: I like it](https://codeforces.com/codeforces.org/s/87877/images/actions/comment-voteup-blue.png)](https://codeforces.com/blog/entry/52697) \+18 [![Vote: I do not like it](https://codeforces.com/codeforces.org/s/87877/images/actions/comment-votedown-blue.png)](https://codeforces.com/blog/entry/52697) You sound like you are on the right track. The base and mod must be coprime — usually, you just choose a prime base and prime mod anyway. Furthermore, you usually need hash two or more mods to stay safe. This is because of the birthday paradox. Normally people use base 137 and hash in 1e9+7 and 1e9+9. [→](https://codeforces.com/blog/entry/52697) [Reply](https://codeforces.com/blog/entry/52697) \| - \| \| \| \|---\|---\| \| » » [yeputons](https://codeforces.com/profile/yeputons "Grandmaster yeputons") \| 9 years ago, [show](https://codeforces.com/blog/entry/52697) [\#]() \| \| \| \| \|---\|---\| \| » » [![](https://codeforces.com/userpic.codeforces.org/2412/avatar/cfc26825136c163e.jpg)](https://codeforces.com/profile/yeputons) [yeputons](https://codeforces.com/profile/yeputons "Grandmaster yeputons") \| 9 years ago, [hide](https://codeforces.com/blog/entry/52697) [\#](https://codeforces.com/blog/entry/52697#comment-367302 "Link to comment") [^](https://codeforces.com/blog/entry/52697#comment-367252 "Parent comment") \\| [![Vote: I like it](https://codeforces.com/codeforces.org/s/87877/images/actions/comment-voteup-blue.png)](https://codeforces.com/blog/entry/52697) \+13 [![Vote: I do not like it](https://codeforces.com/codeforces.org/s/87877/images/actions/comment-votedown-blue.png)](https://codeforces.com/blog/entry/52697) Base should also be strictly greater than the number of different values an individual element can be. E.g. 137 is enough for English latters, but not enough for arbitrary `char`s. Also, it's good to ensure that all codes of individual elements are between 0 and `base-1` so they do not collide modulo `base` for some random reason. [→](https://codeforces.com/blog/entry/52697) [Reply](https://codeforces.com/blog/entry/52697) \| - \| \| \| \|---\|---\| \| » » [\_Dormammu\_](https://codeforces.com/profile/_Dormammu_ "Expert _Dormammu_") \| 6 years ago, [show](https://codeforces.com/blog/entry/52697) [\#]() \| \| \| \| \|---\|---\| \| » » [![](https://codeforces.com/userpic.codeforces.org/925391/avatar/48e3328b21fdb3b0.jpg)](https://codeforces.com/profile/_Dormammu_) [\_Dormammu\_](https://codeforces.com/profile/_Dormammu_ "Expert _Dormammu_") \| 6 years ago, [hide](https://codeforces.com/blog/entry/52697) [\#](https://codeforces.com/blog/entry/52697#comment-589514 "Link to comment") [^](https://codeforces.com/blog/entry/52697#comment-367252 "Parent comment") \\| [←](https://codeforces.com/blog/entry/52697) Rev. 2 [→](https://codeforces.com/blog/entry/52697) [![Vote: I like it](https://codeforces.com/codeforces.org/s/87877/images/actions/comment-voteup-blue.png)](https://codeforces.com/blog/entry/52697) \-24 [![Vote: I do not like it](https://codeforces.com/codeforces.org/s/87877/images/actions/comment-votedown-blue.png)](https://codeforces.com/blog/entry/52697) :) [→](https://codeforces.com/blog/entry/52697) [Reply](https://codeforces.com/blog/entry/52697) \| \| \| \| \|---\|---\| \| » [bhishma](https://codeforces.com/profile/bhishma "Expert bhishma") \| 9 years ago, [show](https://codeforces.com/blog/entry/52697) [\#]() \| \| \| \| \|---\|---\| \| » [![](https://codeforces.com/userpic.codeforces.org/305276/avatar/83814e515ace8f09.jpg)](https://codeforces.com/profile/bhishma) [bhishma](https://codeforces.com/profile/bhishma "Expert bhishma") \| 9 years ago, [hide](https://codeforces.com/blog/entry/52697) [\#](https://codeforces.com/blog/entry/52697#comment-367357 "Link to comment") \\| [![Vote: I like it](https://codeforces.com/codeforces.org/s/87877/images/actions/comment-voteup-blue.png)](https://codeforces.com/blog/entry/52697) \+21 [![Vote: I do not like it](https://codeforces.com/codeforces.org/s/87877/images/actions/comment-votedown-blue.png)](https://codeforces.com/blog/entry/52697) This topics has been discussed a lot of times. [Where to Use and How not to Use Polynomial String Hashing (PACHOCK,RADOSZEWSKI)](https://www.mii.lt/olympiads_in_informatics/pdf/INFOL119.pdf) [Anti-hash test](https://codeforces.com/blog/entry/4898) [→](https://codeforces.com/blog/entry/52697) [Reply](https://codeforces.com/blog/entry/52697) \| In English In Russian ↑ * ↓ [Codeforces](https://codeforces.com/) (c) Copyright 2010-2026 Mike Mirzayanov The only programming contests Web 2.0 platform Server time: Apr/02/2026 09:45:09 (l2). Desktop version, switch to [mobile version](https://codeforces.com/blog/entry/52697?mobile=true). [Privacy Policy](https://codeforces.com/privacy) \\| [Terms and Conditions](https://codeforces.com/terms) Supported by [![TON](https://codeforces.com/codeforces.org/s/87877/images/ton-100x100.png)](https://ton.org/) User lists ![](https://codeforces.com/codeforces.org/s/87877/images/icons/magnifier-medium.png) ![](https://codeforces.com/codeforces.org/s/87877/images/icons/control-270.png) \| Name \| \|---\|
Readable Markdown	[![Codeforces](https://codeforces.com/codeforces.org/s/87877/images/codeforces-sponsored-by-ton.png)](https://codeforces.com/) [![In English](https://codeforces.com/codeforces.org/s/87877/images/flags/24/gb.png)](https://codeforces.com/blog/entry/52697?locale=en) [![По-русски](https://codeforces.com/codeforces.org/s/87877/images/flags/24/ru.png)](https://codeforces.com/blog/entry/52697?locale=ru) → Pay attention → Top rated \| \# \| User \| Rating \| \|---\|---\|---\| \| 1 \| [Benq](https://codeforces.com/profile/Benq "Legendary Grandmaster Benq") \| 3792 \| \| 2 \| [tourist](https://codeforces.com/profile/tourist "Legendary Grandmaster tourist") \| 3755 \| \| 3 \| [ecnerwala](https://codeforces.com/profile/ecnerwala "Legendary Grandmaster ecnerwala") \| 3696 \| \| 4 \| [VivaciousAubergine](https://codeforces.com/profile/VivaciousAubergine "Legendary Grandmaster VivaciousAubergine") \| 3647 \| \| 5 \| [ksun48](https://codeforces.com/profile/ksun48 "Legendary Grandmaster ksun48") \| 3629 \| \| 6 \| [jiangly](https://codeforces.com/profile/jiangly "Legendary Grandmaster jiangly") \| 3616 \| \| 7 \| [turmax](https://codeforces.com/profile/turmax "Legendary Grandmaster turmax") \| 3559 \| \| 8 \| [strapple](https://codeforces.com/profile/strapple "Legendary Grandmaster strapple") \| 3486 \| \| 9 \| [dXqwq](https://codeforces.com/profile/dXqwq "Legendary Grandmaster dXqwq") \| 3436 \| \| 10 \| [Kevin114514](https://codeforces.com/profile/Kevin114514 "Legendary Grandmaster Kevin114514") \| 3427 \| → Top contributors \| \# \| User \| Contrib. \| \|---\|---\|---\| \| 1 \| [Qingyu](https://codeforces.com/profile/Qingyu "Legendary Grandmaster Qingyu") \| 158 \| \| 2 \| [adamant](https://codeforces.com/profile/adamant "Master adamant") \| 153 \| \| 3 \| [Um\_nik](https://codeforces.com/profile/Um_nik "Legendary Grandmaster Um_nik") \| 152 \| \| 4 \| [Dominater069](https://codeforces.com/profile/Dominater069 "Legendary Grandmaster Dominater069") \| 147 \| \| 5 \| [Proof\_by\_QED](https://codeforces.com/profile/Proof_by_QED "International Master Proof_by_QED") \| 145 \| \| 6 \| [errorgorn](https://codeforces.com/profile/errorgorn "Legendary Grandmaster errorgorn") \| 144 \| \| 7 \| [cry](https://codeforces.com/profile/cry "International Master cry") \| 140 \| \| 8 \| [YuukiS](https://codeforces.com/profile/YuukiS "International Grandmaster YuukiS") \| 135 \| \| 8 \| [TheScrasse](https://codeforces.com/profile/TheScrasse "Grandmaster TheScrasse") \| 135 \| \| 10 \| [awoo](https://codeforces.com/profile/awoo "Grandmaster awoo") \| 134 \| → Find user → Recent actions - [szawinis](https://codeforces.com/profile/szawinis) - [Blog](https://codeforces.com/blog/szawinis) - [Teams](https://codeforces.com/teams/with/szawinis) - [Submissions](https://codeforces.com/submissions/szawinis) - [Groups](https://codeforces.com/groups/with/szawinis) - [Contests](https://codeforces.com/contests/with/szawinis) [szawinis's blog](https://codeforces.com/blog/szawinis) Picking the base and mod for string hashing is very important in decreasing the probability of hash collisions. How much are the guidelines affected by the problem itself? So far, I've read that the base should be larger than the alphabet, and the mod should be really large (but not overflow). But is there anything else?
Shard	70 (laksa)
Root Hash	17282934374156394870
Unparsed URL	com,codeforces!/blog/entry/52697 s443