Submission #19413

#	TimeUTC-0	Username	Problem	Language	Result	Execution time	Memory
19413	2016-02-24 11:28:22	imsifile	Ω (kriii4_P3)	C++98	100 / 100	0 ms	1084 KiB

P3

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#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;
double pr, d2[111];
int main(){
  int n, i;
  scanf("%lld%lld%d%d", &p, &q, &n, &k);
  if(k==0){puts("0"); return 0;}
  if(k==n){puts("1"); return 0;}
  if(p==q){puts("0"); return 0;}
  if(q==0){puts("1"); return 0;}
  pr = (double)q/p;
  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;
 
 
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• Subtask 1: 100 / 100