Submission #3426889

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Source Code Expand

#include <vector>
#include <iostream>
using namespace std;
const long long mod = (1e9) + 7;

long long mod_inv(long long x){
  long long k = mod - 2, ret = 1;
  while(k){
    if(k&1){
      ret *= x;
      ret %= mod;
    }
    x *= x;
    x %= mod;
    k >>= 1;
  }
  return ret;
}

int main(){
  long long n, k;
  cin >> n >> k;
  vector<long long> F(n+k);
  F[0] = 1;
  for(int i = 1; i < n+k; ++i) F[i] = (F[i-1]*i)%mod;
  cout << (((F[n+k-1]*mod_inv(F[k]))%mod)*mod_inv(F[n-1]))%mod << endl;
  return 0;
}

Submission Info

Judge Result