Educational 106 problem D time limit and hacks

Revision en2, by thematdev, 2021-03-19 19:29:02

Hi, Codeforces! I have 13 successful hacks of problem D on last round, and also my solution are TLed(probably on one of my tests :)), and i am going to show you, how does it work.

So we have two part of solution.

Solution and complexity

Now we will try to adjust numbers $$$c, d, x$$$ to hack $$$O(t\sqrt{x} \log x + N \log \log N)$$$ solution. Because we are counting distinct prime factors of numbers like $$$\frac{\frac{x}{d_x} + d}{c}$$$, we will use $$$c = 1$$$. And we are factorizing $$$x$$$. So the first idea is to find $$$x$$$ with biggest divisors number, and that $$$x$$$ is $$$8648640$$$. And then we will try to maximize

$$$\sum\limits_{d_x \mid x} s(x/d_x + d)$$$

where $$$s(n)$$$ -- sum of powers of primes in factorization of $$$n$$$(exactly that much operations we do).

And we have first powerful hack. 10000 tests with $$$c=1, d=x=8648640$$$. List of successful hacks using this method below

Tags educational round, #number theory, hacks

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ru2 Russian thematdev 2021-03-19 20:42:03 47 (опубликовано)
ru1 Russian thematdev 2021-03-19 20:40:52 3063 Первая редакция перевода на Русский (сохранено в черновиках)
en9 English thematdev 2021-03-19 20:11:43 0 (published)
en8 English thematdev 2021-03-19 20:08:17 203
en7 English thematdev 2021-03-19 20:02:34 10
en6 English thematdev 2021-03-19 19:57:46 1566
en5 English thematdev 2021-03-19 19:43:25 52 Reverted to en3
en4 English thematdev 2021-03-19 19:40:39 52
en3 English thematdev 2021-03-19 19:36:55 2072
en2 English thematdev 2021-03-19 19:29:02 664 Tiny change: '} + d}{c}$\n\n\n\n\n' -> '} + d}{c}$, we will use $c = 1$.\n\n\n\n\n'
en1 English thematdev 2021-03-19 19:18:15 1065 Initial revision (saved to drafts)