Random decreasing function_SOLVED

/*

CODECHEF

PROBLEM CODE : RDF

*/

#include <stdio.h>

inline int getn() 

{

  int n=0, c=getchar_unlocked();

  while(c < '0' || c > '9') 

      c = getchar_unlocked();

  while(c >= '0' && c <= '9')

      n = (n<<3) + (n<<1) + c - '0', c = getchar_unlocked();

  return n;

}

double a[100001][31] = {{0}};

int main()
{

int T = getn(), N, K, i,j;

a[2][1] = 0.5, a[3][1] = 1.0, a[3][2] = 1.0/6.0;

 

for(i = 4; i < 100001; i++) 

{

  for(j = 1; j <= 30 && j < i; j++)

   {

    if(j == 1) 

      a[i][j] = a[i-1][j] + 0.5;

    else a[i][j] = (a[i-1][j-1] + a[i-1][j]*(i-1))/(double)i;

    if(a[i][j] <= 1.0/500000.0) 

      break;

   }

}

while(T--)

 {

   N = getn(), K = getn();

   if(!K) 

     printf("%d\n",N);

   else if(K <= 30 && N > K) 

    printf("%.7lf\n",a[N][K]);

   else 

    printf("0\n");

  } 

return 0;

}