Submission #21420

#	Time	Username	Problem	Language	Result	Execution time	Memory
21420		gs14004	순열 (kriii4_T)	C++11	100 / 100	203 ms	2020 KiB

T

#include <bits/stdc++.h>
using namespace std;
typedef long long lint;
typedef long double llf;
typedef pair<int, int> pi;
const int mod = 1e9 + 7;

lint ipow(lint x, lint p){
	lint ret = 1, piv = x % mod;
	while(p){
		if(p&1) ret *= piv;
		piv *= piv;
		ret %= mod;
		piv %= mod;
		p >>= 1;
	}
	return ret % mod;
}

int n, k;

int main(){
	cin >> n >> k;
	lint ans = 0;
	for(int i=k+1; i<=n; i++){
		ans += (n - i + 1) * ipow(i+1, mod - 2) % mod;
		ans %= mod;
	}
	for(int i=2; i<=n+1; i++) ans = (ans * i) % mod;
	cout << ans;
}

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