Submission #19385

#	Time	Username	Problem	Language	Result	Execution time	Memory
19385		imsifile	Ω (kriii4_P3)	C++98	0 / 100	0 ms	1084 KiB

P3

#include<stdio.h>
#define mod 1000000007

typedef long long lld;
lld a, b, sum;

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;
}

int n, k;
lld p, q, pq, mpq, dy[111], re;

int main(){
	int n, i;
	scanf("%lld%lld%d%d", &p, &q, &n, &k);
	pq = q*exp(p,mod-2)%mod, mpq = (mod-pq)%mod;
	dy[1]=1;
	for(i=1; i<n; i++)dy[i+1] = (dy[i] + mpq*dy[i-1]%mod)*exp(1+mpq, mod-2)%mod;
	dy[1] = exp(dy[n],mod-2);
	for(i=1; i<n; i++)dy[i+1] = (dy[i] + mpq*dy[i-1]%mod)*exp(1+mpq, mod-2)%mod;
	printf("%lld", dy[k]);
	return 0;
}

• Subtask 1: 0 / 100