Given a collection of numbers, return all possible permutations. For example,[1,2,3] have the following permutations:[1,2,3], [1,3,2], [2,1,3], [2,3,1], [3,1,2], and [3,2,1]. 实现思想: 给定一个数组[1,2,3,4] 1.[1,[2,3,4]] ---------->[2,3,4]的子数组计算--->[2,[3,4]],…