从集合的角度看,从n个不同元素中取出m(m≤n)个元素的排列(组合),可以组成一个集合,其中每一个排列(组合)是它的一个元素,其排列数(组合数)就是这个集合中的元素的个数.因此在许多排列组合问题中适当构造集合,将问题中的条件关系转化为可用集合图形表示出来的集合间的运算关系, From a collective point of view, it is possible to form a set in which the arrangement (combination) of m (m ≦ n) elements is taken out of n different elements in which each arrangement (combination) is an element thereof, the arrangement number Number) is the number of elements in this set, so in many of the permutation and combination of appropriate set of questions, the question of the relationship between the conditions can be converted to a collection of graphics can be expressed by the set of computational relations,