Submission #2435800

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Source Code Expand

#include <bits/stdc++.h>
using namespace std;
#define REP(i,n) for (int i=0;i<(n);i++)
#define int long long
#define MOD 1000000007


int fact(int x){
    int k=1;
    REP(i,x){
        k=(k*(i+1))%MOD;
    }
    return k;
}

int BE(int b,int e){//binary exponentiation
    if(e==0){
        return 1;
    }else{
        int sum = BE(b,e/2);
        if(e%2==0){
            return (sum*sum)%MOD;
        }else{
            return (((sum*sum)%MOD)*b)%MOD;
        }
    }
}


signed main(){
    int N,K;
    int p,q,r;
    cin >> N >> K;
    
    
    if(N>K){
        p=fact(N+K-1);
        q=fact(K);
        r=fact(N-1);
    }else{
        p=fact(N);
        q=fact(K%N);
        r=fact(N-(K%N));
    }
    q=BE(q,MOD-2);
    r=BE(r,MOD-2);
    p = (p*q)%MOD;
    p = (p*r)%MOD;
    cout << p << endl;
    return 0;
}

Submission Info

Judge Result