“至少或至多”型排列组合应用题比较抽象,求解时往往容易发生重复和遗漏的现象.在直接考虑分类讨论较繁时,一方面可从问题的反面入手,采用间接法求解.另一方面也可转换角度考虑问题,将其转化为与之等价的问题来解,从而获得原问题的解.本文旨在介绍这类问题的几种常见方法.一、 “At least or at most” type of combination and application problems are relatively abstract, and they are often prone to duplication and omission when solving. When the classification discussion is more complicated, one can start from the opposite side of the problem and use the indirect method to solve it. On the other hand, You can also consider the problem by converting it into an equivalent problem, so as to obtain the solution to the original problem. This article aims to introduce several common methods of this type of problem.