### Deemo's blog

By Deemo, history, 6 years ago,

Can anyone tell me how to solve this problem?

http://codeforces.com/contest/177/problem/G2

 » 6 years ago, # | ← Rev. 5 →   +13 Let's calculate for each prefix s[1..i] the minimum fibonacci index minind[i] such that s[1..i] is a suffix of fib[i] and s[i + 1..n] is a prefix of fib[i + 1]. Because the relation fib[i] = fib[i - 1]fib[i - 2]can be written equivalently as: fib[i] = fib[i - 2]fib[i - 3]fib[i - 2]it follows that $min_ind[i]$ is either ∞ or less than n (because fib[i] has all the prefixes of fib[i - 2]). After that, it is essentially a linear reccurence of type DP[i] = DP[i - 1] + DP[i - 2] + occurences_less_than_inffor all $\i \geq n$ (or n + 2 or smth.). You basically have to compute DP[n] and DP[n + 1] and occurences_less_than_inf, and then do matrix exp. I think that should work :).