LeetCode- permutations

最新推荐文章于 2020-04-18 12:42:57 发布

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博客围绕给定数字集合求所有可能排列展开，以[1,2,3]为例，给出了其全排列结果，如[1,2,3]、[1,3,2]等，属于信息技术领域的算法问题。

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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].

import java.util.*;
 
public class Solution {
    public ArrayList<ArrayList<Integer>> permute(int[] num) {
        ArrayList<ArrayList<Integer>> retList = new ArrayList<ArrayList<Integer>>();
        if (num == null || num.length == 0)
            return retList;
        ArrayList<Integer> list = new ArrayList<Integer>();
        boolean[] visited = new boolean[num.length];
        dfs(num, visited, list, retList);
        return retList;
    }
    private void dfs(int[] nums, boolean[] visited, ArrayList<Integer> list, ArrayList<ArrayList<Integer>> retList) {
        if (list.size() == nums.length) {
            retList.add(new ArrayList<Integer>(list));
        } else {
            for (int i = 0; i < nums.length; i++) {
                if (!visited[i]) {
                    visited[i] = true;
                    list.add(nums[i]);
                    dfs(nums, visited, list, retList);
                    list.remove(list.size() - 1);
                    visited[i] = false;
                }
            }
        }
    }
     
}