Submission #19255

#	Time	Username	Problem	Language	Result	Execution time	Memory
19255		kaTkaHr	순열 (kriii4_T)	C++14	8 / 100	2000 ms	1084 KiB

T

#include <stdio.h>
#include<vector>
#include <algorithm>
#include <map>

using namespace std;

typedef long long ll;

const int MX = 105, MM = 1000000007;

ll rv(ll A){
    ll R = 1, B = MM-2;
    while(B){
        if( B&1 ) R = R * A % MM;
        A = A * A % MM; B /= 2;
    }
    return R;
}

struct frac{
    ll A, B;
		frac(ll A):A(A), B(1){}
    frac(ll a, ll b){
        A = (a%MM+MM) % MM;
        B = (b%MM+MM) % MM;
    }
    frac(){A = 0, B = 1;}
    frac operator+ (const frac &l)const{
        return frac((A * l.B + B * l.A) % MM, B * l.B % MM);
    }
    frac operator*(const frac &l)const{
        return frac(A*l.A % MM, B*l.B % MM);
    }
    frac operator/(const frac &l)const{
        return frac(A*l.B % MM, B*l.A % MM);
    }
    frac operator- (const frac &l)const{
        return frac((A*l.B - B*l.A%MM + MM) % MM, B*l.B % MM);
    }
    ll v(){ return A * rv(B) % MM; }
};

int main()
{
	int N, KK;
	scanf("%d%d", &N, &KK); 
	frac tot = 0;
	for(int K = KK+1; K <= N; K++){
		frac ans = 0, mul = 1;
		for(int i = 1; i <= N; i++){
			mul = mul * i;
		}
		for(int i = N; i >= 1; i--){
			mul = mul / i;
			ans = ans + mul * (N-i+1);
			mul = mul * (i-K);
		}
		ans = ans * K * (N-K+1);
		tot = ans + tot;
	}
	printf("%lld\n", tot.v());
}

• Subtask 1: 8 / 8
• Subtask 2: 0 / 92