[解题报告]530 Binomial Showdown

  Binomial Showdown 

In how many ways can you choose k elements out of n elements, not taking order into account?

Write a program to compute this number.

Input Specification 

The input file will contain one or more test cases.

Each test case consists of one line containing two integers n () and k ( ).

Input is terminated by two zeroes for n and k.

Output Specification 

For each test case, print one line containing the required number. This number will always fit into an integer, i.e. it will be less than 2³¹.

Warning: Don't underestimate the problem. The result will fit into an integer - but if all intermediate results arising during the computation will also fit into an integer depends on your algorithm. The test cases will go to the limit.

Sample Input 

4 2
10 5
49 6
0 0

Sample Output 

6
252
13983816



排列组合嘛。。。注意数据类型

#include<stdio.h>
int main()
{
    int a,b,n,m;
    double s;
    while(scanf("%d %d",&n,&m)!=EOF)
    {
        if(n==0) break;
        if(m>n/2) m=n-m;
        for(a=1,b=n,s=1;a<=m;a++,b--)
        {
         s=s*b;
         s=s/a;
        }
        printf("%.0lf\n",s);
    }
    return 0;
}