In mathematics, a combination is a selection of items from a collection, such that the order of selection does not matter (unlike permutations). To choose m items from a total item of n, the formula for combination is as follows:

Given N football teams (8 <= N <= 32), and each team will play m ( 2 <= m <=4 ) games with any other team.

Sample Input:

N = 8, m= 3

Sample Output:

84

For 8 teams each needs to play 3 games with another team. The total games are 84.

数据结构和算法：初级练习题 #60 阶乘和组合（一）

组合（combination），数学的重要概念之一。从n个不同元素中每次取出m个不同元素（0≤m≤n），不管其顺序合成一组，称为从n个元素中不重复地选取m个元素的一个组合。所有这样的组合的总数称为组合数，这个组合数的计算公式为

给定N支足球队 (8 <= N <= 32)，每支球队都需要和其他每个球队比赛m场 ( 2 <= m <=4 )，计算总共有多少场比赛。

输入样例：

N = 8, m= 3

输出样例：

84

八支球队相互之间都需要比赛三场，总共的比赛是84场。

Python Solution