排列与组合是解决计数问题的一种强有力的工具.由于组合数学逐渐受到人们的青睐,因此,排列、组合的应用越来越广泛.对于排列、组合应用问题,首先要分清元素与位置的关系,特殊元素和特殊位置要优先考虑.对于含有多个约束条件的排列、组合应用问题,往往以一个约束条件为主进行讨 Arranging and combining is a powerful tool to solve the counting problem. As combinatorial mathematics is gradually favored by people, the application of permutation and combination is becoming more and more widespread. For the problems of permutation and combinational application, we must first distinguish the elements and positions. Relationships, special elements, and special locations should be given priority. For arrangements with multiple constraints, combinatorial application problems are often discussed with a constraint condition.