picking balls.txt

以前ACM在哈工程HRBEU做的一些简单题目

#include <stdio.h>
#include <iostream.h>
long long sss(long long n,long long r)
{
     long long i,j,sum=1;
     if(r>n/2)r=n-r;
     for(i=n,j=1;j<=r;i--,j++)
        sum=sum*i/j;
        return sum;
}
int main()
{
    long long n,k,a[51],b[51],sum,c,d;
    int i,j;
    while(cin>>n>>k)
    {
      if(n==-1||k==-1)break;
      bool sign=true;
      sum=0;
      for(i=0;i<n;i++){cin>>a[i];sum+=a[i];}
      for(i=0;i<n;i++)cin>>b[i];
      if(n!=0&&k!=0)
      {
          c=1;
               d=sss(sum,k);
               for (i=0;i<n;i++)
                   if (b[i]!=0)
                   {
                       if (b[i]>a[i])
                       {
                           sign=false;
                           break;
                       }       
                      else
                          c=c*sss(a[i],b[i]);
                }
              if (sign)
                      printf("%.5f\n",1.0*c/d);
              else
                      printf("0.00000\n");
      }
      else
      {
          
            if (n==0)
            {
                if (k!=0)
                    printf("0.00000\n");
                   else
                       printf("1.00000\n");
            }
            else
                printf("1.00000\n");
        }
        scanf(" ");
        }
        return 0;
}