Submission #4276093

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Source Code Expand

#include <bits/stdc++.h>
#define int long long
using namespace std;
const int MOD=1e9+7;
std::vector<int> v(1000);

int pw(int a,int b){
  int res=1,k=a;
  while(b){
    if(b%2)res*=k;res%=MOD;
    b/=2;
    k*=k;k%=MOD;
  }
  return res;
}
int kma(int n,int k){
  if(n<=k)return 1;
  int res=v[n];
  res*=pw(v[k],MOD-2);res%=MOD;
  res*=pw(v[n-k],MOD-2);res%=MOD;
  return res;
}

signed main(){
  int N,K;cin>>N>>K;
  v[0]=1;for(int i=1;i<1000;i++)v[i]=v[i-1]*i%MOD;
  if(N>K)cout<<kma(N+K-1,K)<<endl;
  else cout<<kma(N,K%N)<<endl;
}

Submission Info

Judge Result