Submission #19990

#	Time	Username	Problem	Language	Result	Execution time	Memory
19990		ainta	순열 (kriii4_T)	C++98	100 / 100	891 ms	16864 KiB

T

#include<stdio.h>
#include<algorithm>
using namespace std;
int n, K;
long long F[1010000], InvF[1010000], Mod = 1000000007, Res;
long long Pow(long long a, int b){
    long long r = 1;
    while(b){
        if(b&1)r=r*a%Mod;
        a=a*a%Mod;b>>=1;
    }
    return r;
}
int main(){
    int L, i;
    scanf("%d%d",&n,&K);
    F[0]=InvF[0]=1;
    for(i=1;i<=n+1;i++){
        F[i]=F[i-1]*i%Mod;
        InvF[i] = Pow(F[i],Mod-2);
    }
    for(L=K+1;L<=n;L++){
        Res = (Res + F[L]*F[n-L+1]%Mod*F[n+1]%Mod*InvF[L+1]%Mod*InvF[n-L])%Mod;
    }
    printf("%lld\n",Res);
}

• Subtask 1: 8 / 8
• Subtask 2: 92 / 92