题解 | Java-回溯-#有重复项数字的所有排列#

import java.util.*;

public class Solution {
    LinkedList<Integer> tmp = new LinkedList<>();
    ArrayList<ArrayList<Integer>> res = new ArrayList<>();
    public ArrayList<ArrayList<Integer>> permuteUnique(int[] num) {
        int n = num.length;
        Arrays.sort(num); // 排序方便字典序上升
        dfs(num);
        return res;
    }
    
    public void dfs(int[] num){
        int n = num.length;
        if (tmp.size() == n) { // 递归出口
            ArrayList<Integer> list = new ArrayList<>();
            for (int i : tmp) {
                list.add(num[i]);
            }
            res.add(list);
            return;
        }
        boolean[] visit = new boolean[7]; // -1 --> 5 。记录该层此数字有没有被遍历过
        for (int i = 0; i < n; ++i) {
            if (tmp.contains(i) || visit[num[i] + 1]) continue;
            tmp.add(i);
            visit[num[i] + 1] = true;
            dfs(num);
            tmp.removeLast();
        }
    }
}