Submission #19312

#	TimeUTC-0	Username	Problem	Language	Result	Execution time	Memory
19312	2016-02-24 09:26:19	ainta	Ω (kriii4_P3)	C++98	100 / 100	0 ms	1084 KiB

P3

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#include<stdio.h>
long long Mod = 1000000007, P, Q, N, K, C[110][2], Res[110];
long long Inv(long long a){
    long long b = Mod - 2, r = 1;
    while(b){
        if(b%2)r=r*a%Mod;
        a=a*a%Mod;b/=2;
    }
    return r;
}
int main(){
    int i;
    scanf("%lld%lld%lld%lld",&P,&Q,&N,&K);
    C[1][0] = 0, C[1][1] = (P-Q)*Inv(P)%Mod;
    for(i=1;i+1<N;i++){
        C[i+1][0] = Q*C[i][0]%Mod*Inv((P-C[i][1]*Q%Mod+Mod)%Mod)%Mod;
        C[i+1][1] = (P-Q)%Mod*Inv((P-C[i][1]*Q%Mod+Mod)%Mod)%Mod;
    }
    Res[N] = 1;
    for(i=N-1;i>=1;i--){
        Res[i] = (Res[i+1]*C[i][1]+C[i][0])%Mod;
    }
    printf("%lld\n",Res[K]);
}
 
 
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• Subtask 1: 100 / 100