题解 | 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<>>
     */
     ArrayList<ArrayList<Integer>> res = new ArrayList<>();
    public ArrayList<ArrayList<Integer>> permuteUnique (int[] num) {
        // write code here
        Arrays.sort(num);
        boolean[] visited = new boolean[num.length]; 
        backTrace(num,visited, new ArrayList<Integer>());
        return res;
    }

    private void backTrace(int[] num,  boolean[] visited, ArrayList<Integer> list) {
        if (list.size() == num.length) {
            res.add(new ArrayList<>(list));
            return;
        }

        for (int i=0; i<num.length; i++) {
            if (visited[i]) continue;
            if (i > 0 && num[i] == num[i-1] && !visited[i-1]) continue;
            list.add(num[i]);
            visited[i] = true;
            backTrace(num,  visited, list);
            visited[i] = false;
            list.remove(list.size()-1);
        }
    }
}