LeetCode——Permutations

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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].

原题链接：https://oj.leetcode.com/problems/permutations/

题目：给定一组数，返回其全排列。

思路：记录每一个数是否被使用过，将未使用过的数加入到current中，current长度已满，则加入到result中。

public List<List<Integer>> permute(int[] num) {if (num == null)return null;List<List<Integer>> result = new ArrayList<List<Integer>>();if (num.length == 0)return result;permute(num, new boolean[num.length], new ArrayList<Integer>(), result);return result;}public void permute(int[] num, boolean[] isused,ArrayList<Integer> current, List<List<Integer>> result) {if (current.size() == num.length) {result.add(new ArrayList<Integer>(current));return;}for (int i = 0; i < num.length; i++) {if (!isused[i]) {isused[i] = true;current.add(num[i]);permute(num, isused, current, result);current.remove(current.size() - 1);isused[i] = false;}}}

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