Submission #19205

#	TimeUTC-0	Username	Problem	Language	Result	Execution time	Memory
19205	2016-02-20 15:37:42	kriii	Ω (kriii4_P3)	C++14	100 / 100	0 ms	1084 KiB

P3

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#include <stdio.h>
const long long mod = 1000000007;
long long fpow(long long a, long long p)
{
  a = (a % mod + mod) % mod;
  p = (p % (mod - 1) + mod - 1) % (mod - 1);
  long long r = 1;
  while (p){
    if (p & 1) r = r * a % mod;
    a = a * a % mod;
    p >>= 1;
  }
  return r;
}
int main()
{
  int P,Q,N,K; scanf ("%d %d %d %d",&P,&Q,&N,&K);
  if (K == 0) puts("0");
  else if (K == N) puts("1");
  else if (Q == 0) puts("1");
  else if (Q == P) puts("0");
  else{
    long long v[101];
    long long pr = Q * fpow(P,-1) % mod, rv = fpow(1-pr,-1);
    v[0] = 0; v[1] = 1;
    for (int i=2;i<=N;i++) v[i] = ((v[i-1] - pr * v[i-2]) % mod * rv % mod + mod) % mod;
 
 
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• Subtask 1: 100 / 100