Submission #20101

#	Time	Username	Problem	Language	Result	Execution time	Memory
20101		imsifile	순열 (kriii4_T)	C++98	100 / 100	821 ms	16724 KiB

T

#include<stdio.h>
#include<memory.h>
#define mod 1000000007
#define inv(a) exp(a,mod-2)

typedef long long lld;

lld exp(lld a, lld b){
	if(b==0)return 1;
	lld k=exp(a, b/2);
	k=(k*k)%mod;
	if(b%2)k=(k*a)%mod;
	return k;
}

lld fac[1001001], rfac[1001001];

void init(){
	lld i;
	fac[0]=rfac[0]=1;
	for(i=1; i<=1000001; i++){
		fac[i]=(fac[i-1]*i)%mod;
		rfac[i]=inv(fac[i]);
	}
}

lld comb(lld a, lld b){
	return fac[a]*rfac[b]%mod*rfac[a-b]%mod;
}

lld n, k, sum;

int main(){
	lld i;
	init();
	scanf("%lld%lld", &n, &k);
	for(i=k+1; i<=n; i++){
		lld im = fac[n+1]*(n-i+1)%mod * inv(i+1);
		im = (im%mod+mod)%mod;
		sum += im, sum%=mod;
	}
	printf("%lld", sum);
	return 0;
}

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