Theres a problem from the [The ICPC 2018 — Vietnam Central Provincial Contest](http://acmvncenter2018.tk/contest/index.php?cid=ICPCVNC18) that supposedly involves some combinatorics (The problem is [here](http://acmvncenter2018.tk/contest/problem.php?cid=ICPCVNC18&probid=K))↵
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I originally planned to count the ways to break N/K into sum of at most M numbers, and then count the number of permutations of the children for each ways, and then use binpow to calculate total_ways % 1e9+7 (probably the first thing you would think of when you see the problem). But the limit was so high that i will have to choose between ridiculously long running time or using bignum (which can cause either TLE or MLE, whatever comes first.)↵
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So it would be better if i could have an O(1) or an O(log N/K) solution for this problem.↵
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Thanks.↵
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Edit: the editorial is 4 pages long and it is imn Vietnamese, and i don't understand it either
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I originally planned to count the ways to break N/K into sum of at most M numbers, and then count the number of permutations of the children for each ways, and then use binpow to calculate total_ways % 1e9+7 (probably the first thing you would think of when you see the problem). But the limit was so high that i will have to choose between ridiculously long running time or using bignum (which can cause either TLE or MLE, whatever comes first.)↵
↵
So it would be better if i could have an O(1) or an O(log N/K) solution for this problem.↵
↵
Thanks.↵
↵
Edit: the editorial is 4 pages long and it is i
