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package com.yangchd.leetcode.medium;

import java.util.*;

/**

* @author yangchd 2018/9/12.

*

* 46. Permutations

* Given a collection of distinct integers, return all possible permutations.

*

* Example:

* Input: [1,2,3]

* Output:

* [

* [1,2,3],

* [1,3,2],

* [2,1,3],

* [2,3,1],

* [3,1,2],

* [3,2,1]

* ]

*/

public class Permutations {

class Solution {

public List<List<Integer>> permute(int[] nums) {

List<List<Integer>> list = new ArrayList<List<Integer>>();

if (nums == null || nums.length == 0) {

return list;

}

backtrack(list, 0, nums);

return list;

}

private void backtrack(List<List<Integer>> list, int start, int[] nums) {

if (start == nums.length) {

List<Integer> temp = new ArrayList<Integer>();

for (int num : nums) {

temp.add(num);

}

list.add(new ArrayList<Integer>(temp));

return;

}

for (int i = start; i < nums.length; i++) {

swap(nums, start, i);

backtrack(list, start + 1, nums);

swap(nums, start, i);

}

}

private void swap(int[] nums, int i, int j) {

int temp = nums[i];

nums[i] = nums[j];

nums[j] = temp;

}

}

}