[解题报告]530 - Binomial Showdown-优快云博客

本文提供了一个C++程序，用于计算从n个元素中选择k个元素的方法数量，不考虑顺序。程序通过逐步计算并优化过程来避免溢出，并在给定示例输入上验证了其正确性。

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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 ( $n \ge 1$ ) and k ( $0 \le k \le n$ ).

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

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;
}