Submission #48627418

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Source Code Expand

#include<cstdio>
#include<iostream>
#include<algorithm>
#include<cstring>
#define N 20000005
#define ll long long
#define p 1000000007
using namespace std;

inline int power(int a,int t){
    int res = 1;
    while(t){
        if(t&1) res = (ll)res*a%p;
        a = (ll)a*a%p;
        t >>= 1;
    }
    return res;
}

int fac[N],ifac[N],inv[N];

void init(int n){
    fac[0] = fac[1] = ifac[0] = ifac[1] = 1;
    for(int i=2;i<=n;++i) fac[i] = (ll)fac[i-1]*i%p;
    ifac[n] = power(fac[n],p-2);
    for(int i=n-1;i;--i) ifac[i] = (ll)ifac[i+1]*(i+1)%p;
}

inline int binom(int n,int m){
    if(n<m||m<0) return 0;
    return (ll)fac[n]*ifac[m]%p*ifac[n-m]%p;
}

int n,m,ans,bm;
ll _m;

int main(){
    scanf("%d%lld",&n,&_m);
    if(n==1||_m==0){
        puts("1");
        return 0;
    }
    init(n<<1);
    --n,bm = 1,m = _m%p;
    for(int i=1;i<=n;++i){
        ans = (ans+(ll)binom(n,i)*bm%p*binom(n+i,n-m-1+i))%p;
        bm = (ll)bm*(m-i)%p*fac[i-1]%p*ifac[i]%p;
    }
    printf("%lld",(ll)(ans+p)*fac[n-1]%p*ifac[n]%p);
    return 0;   
}

Submission Info

Compile Error

Main.cpp: In function ‘int main()’:
Main.cpp:38:10: warning: ignoring return value of ‘int scanf(const char*, ...)’ declared with attribute ‘warn_unused_result’ [-Wunused-result]
   38 |     scanf("%d%lld",&n,&_m);
      |     ~~~~~^~~~~~~~~~~~~~~~~

Judge Result