How to implement php

Question

算法，php如何实现输入一个字符串，输出该字符串中字符的所有组合。
例如：输入参数：字符串："abc"
输出："a","b","c","ab","ac","bc","abc"

Answer 1

From the perspective of the problem, it needs to be implemented using a recursive algorithm. Of course, it can also be implemented indirectly using static variables