题解 | #没有重复项数字的全排列#

import java.util.*;


public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param num int整型一维数组 
     * @return int整型ArrayList<ArrayList<>>
     */
    public ArrayList<ArrayList<Integer>> permute (int[] num) {
        // write code here
        int length = num.length;
        ArrayList<ArrayList<Integer>> lists = new ArrayList<> ();
        if(length == 0) return lists;
        Stack<Integer> path = new Stack<>();
        boolean[] isUsed = new boolean[length];
        dfs(num, length, 0, path, isUsed, lists);
        return lists;
    }

    private static void dfs(int[] num, int len, int depth, Stack<Integer> path, boolean[] isUsed, ArrayList<ArrayList<Integer>> lists){
        if(depth == len){
            lists.add(new ArrayList<Integer>(path));
            return;
        }else{
            for(int i = 0; i < len; i++){
                if(isUsed[i])  continue;
                path.add(num[i]);
                isUsed[i] = true;
                dfs(num, len, depth+1, path, isUsed, lists);
                isUsed[i] = false;
                path.pop();
            }
        }
    }
}