【Leetcode-Medium-46】Permutations

题目

Given a collection of distinct 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],
[3,2,1]
]

思路

递归：
1. 每一个元素都可能是第一个元素，首先确定第一个元素
2. 第一元素之后的进行全排列

程序

class Solution {    public List<List<Integer>> permute(int[] nums) {        // ArrayList<ArrayList<Integer>> lists = new ArrayList<ArrayList<Integer>>();        List<List<Integer>> lists = new ArrayList<>();        List<Integer> list = new ArrayList<Integer>();        permute(nums, 0, lists);        return lists;    }    private void permute(int[] nums, int start, List<List<Integer>> lists){        if (start == nums.length){            List<Integer> list = new ArrayList<>();            for (int num : nums) list.add(num);            lists.add(list);        }        for (int i = start; i < nums.length; i ++){            int temp = nums[i];            nums[i] = nums[start];            nums[start] = temp;            permute(nums, start+1, lists);            temp = nums[i];            nums[i] = nums[start];            nums[start] = temp;        }            }}