BIbicsi·Nov 14, 2023
As a competitive programmer, I’ve seen similar ‘magic’ tricks (including this one) here: https://github.com/kth-competitive-programming/kactl/blob/ma... (page 23, 10.5.1)
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kactl
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kth-competitive-programming / kactl
kactl
KTH Algorithm Competition Template Library (... eller KTHs AC-tillverkande lapp)
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KTH Algorithm Competition Template Library (... eller KTHs AC-tillverkande lapp)
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This week on Hacker News
Nov 7–Nov 14 UTC · Direct repository links and separately labeled related project stories. Indexed through 11/14/2026, 1:49:46 PM UTC.
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HN mentions by year4 dated mentions
Observed mentions: 2020-05-29 21:30:52 UTC to 2023-11-14 17:11:59 UTC.
Counts come from the repository’s dated source evidence. Index cutoff: 2026-11-02 08:16:59 UTC.
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| Period | Start (UTC) | End (exclusive, UTC) | Mentions | Submissions | Comments |
|---|---|---|---|---|---|
| 2020 | 2020-01-01 00:00:00 UTC | 2021-01-01 00:00:00 UTC | 2 | 1 | 1 |
| 2021 | 2021-01-01 00:00:00 UTC | 2022-01-01 00:00:00 UTC | 1 | 0 | 1 |
| 2022 | 2022-01-01 00:00:00 UTC | 2023-01-01 00:00:00 UTC | 0 | 0 | 0 |
| 2023 | 2023-01-01 00:00:00 UTC | 2024-01-01 00:00:00 UTC | 1 | 0 | 1 |
What Hacker News says
4 sourcesThere's not _that_ many algorithms or data structures you see in competitive programming, and the vast majority of them aren't advanced. You do need to memorize a good portion of them, but doing so is the easy part towards becoming good at it.
You can read one moderate length book and know all of the DSes and algorithms you'll need for 99.9% of the time. cses.fi/book is a good one with a free version if you're curious.
https://github.com/kth-competitive-programming/kactl may also be of interest, it contains a good amount of the algorithms/DSes you'd ever need on a few printable pages (20ish).
In Competitive programming is uselessI was reading about an implementation of Barrett reduction recently:
https://en.wikipedia.org/wiki/Barrett_reduction
Specifically one that uses 80-bit long double for calculating `(__int128_t)a * b % M` from this github:
https://github.com/kth-competitive-programming/kactl/blob/ma...
But how do you test the correctness of such code? You can't just stress test all possible product of 64 bit numbers!
In the end you still gotta go back to good old fashion proofs:
https://github.com/kth-competitive-programming/kactl/blob/ma...
In There are only four billion floats, so test them all (2014)Show HN: High quality source of algorithms/DS for competitive programming
https://github.com/kth-competitive-programming/kactl/blob/master/kactl.pdf
I've occasionally seen sources of algorithms/data structures posted on HN, but they've mostly been fairly low quality. This source was created/maintained for the International Collegiate Programming Competition, which has a 25 page limit.
Among others, the last 3 MIT ICPC teams have used a variant of this notebook.
Some neat things in this notebook:
The fastest 64 bit mod mul implementation I've seen (uses doubles and proven correct): https://github.com/kth-competitive-programming/kactl/blob/master/content/number-th…
A fast/short implementation of FFT: https://github.com/kth-competitive-programming/kactl/blob/master/content/numerical…
A bump allocator: https://github.com/kth-competitive-programming/kactl/blob/master/content/vario
Read the rest
us/BumpAllocator.h