Submission #19588

#	TimeUTC-0	Username	Problem	Language	Result	Execution time	Memory
19588	2016-02-24 22:01:12	gs12117	Ω (kriii4_P3)	C++98	100 / 100	0 ms	1084 KiB

P3

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#include<stdio.h>
int mod=1000000007;
int p,q,n,m;
int a[110];
int b[110];
long long int f(long long int x,long long int y){
  if(y==0)return 1;
  long long int r=f(x,y/2);
  r*=r;
  r%=mod;
  if(y%2==0)return r;
  r*=x;
  r%=mod;
  return r;
}
int main(){
  int i;
  long long int res=0;
  scanf("%d%d%d%d",&p,&q,&n,&m);
  p=(p-q)*f(p,mod-2)%mod;
  b[1]=p;
  for(i=1;i<n;i++){
    b[i+1]=p*f(((long long int)b[i]*((p+mod-1)%mod)%mod+1)%mod,mod-2)%mod;
  }
  a[n]=1;
  for(i=n-1;i>0;i--){
    a[i]=(long long int)a[i+1]*b[i]%mod;
  }
  a[0]=0;
  printf("%d\n",a[m]);
 
 
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• Subtask 1: 100 / 100