Update numtheory.cpp

Changes

1 changed files (+9/-0)

• Math/numtheory.cpp
  • @@ -1,5 +1,7 @@
    constexpr ll MOD = 1e9+7; + int fact[200002] = { 1 }, ifact[200002] = { 1 }; + int pw(int base, int exp) { int res = 1; while (exp) {
  • @@ -11,3 +13,10 @@ int pw(int base, int exp) {
    } int inv(int x) { return pw(x, MOD - 2); } + + int nCr(int n, int k) { return (ll)fact[n] * ifact[k] % MOD * ifact[n - k] % MOD; } + + for (int i = 0; i < n; ++i) { + fact[i + 1] = (i + 1ll) * fact[i] % MOD; + ifact[i + 1] = inv(fact[i + 1]); + }