46. Permutations【LeetCode算法之旅之DFS】

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]
]

题意：求一个序列的各种组合。

思路：使用DFS策略。代码如下：package leetcode;

import java.util.ArrayList;
import java.util.List;

public class Solution {

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

private void dfs(int[] nums, List<Integer> subList){
if(subList.size() == nums.length){
list.add(subList);
return;
}
for (int i = 0; i < nums.length; i++){
if(!subList.contains(nums[i])){
List<Integer> subList2 = new ArrayList<Integer>();
subList2.addAll(subList);//subList2是对subList的复制
subList2.add(nums[i]);
dfs(nums, subList2);
}
}
}

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

List<Integer> subList = new ArrayList<Integer>();
dfs(nums, subList);
return list;
}
}