I was solving this problem with a combinatoric based approach. So I compute binomial coefficient using Fermat Little Th. and modular inverse. I have correct values for N up to 34, then my code starts giving wrong values. I belive the approach is correct but there is some issue I cant figure out related to modulo, modular inverse or powmod function. Can anybody help me understanding why my code fails? CODE

Auto comment: topic has been updated by _doomboo_ (previous revision, new revision, compare).Your C(n, k) function should be:

Spoilerit doesnt work anyway. I tried also approach with pascal triangle to compute nCk but I get the exact same issue: everything is fine for N up to 34, then it starts failing... it's so weird

Nobody able to help? :(

Please help

I might be wrong, but the 70'th line (

`ll half = nCk(n, n/2, mod)/2;`

) might mess your calculations up, maybe that`nCk`

returns an odd number but you divide it by 2. I suggest using`*inverse(2, mod)`

. I haven't verified the code logic so I cannot say if the approach is correct or not. Hope this helps.thank you very much, this is the actual issue. You made my day :D.