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package leetcode;

import com.alibaba.fastjson.JSON;

import org.junit.Test;

import utils.ArrayUtils;

import java.util.ArrayList;

import java.util.List;

/**

* dfs深度遍历，求一个数组的排列组合

* 如，输入1,2,3,输出这三个元素所有的排序组合可能性

*/

public class Permute {

//[[1,2,3],[1,3,2],[2,1,3],[2,3,1],[3,2,1],[3,1,2]]

@Test

public void test() {

System.out.println(JSON.toJSONString(permute(new int[]{1, 2, 3})));

}

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

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

dfs(nums, 0, res);

return res;

}

/**

* 不断交换元素来列出所有可能的排列

*

* @param nums

* @param index

* @param res

*/

private void dfs(int[] nums, int index, List<List<Integer>> res) {

if (index == nums.length) {

List<Integer> list = new ArrayList();

for (int i : nums) list.add(i);

res.add(list);

}

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

ArrayUtils.swap(nums, index, i);

dfs(nums, index + 1, res);

ArrayUtils.swap(nums, index, i);

}

}

}