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<>>
     */
    public ArrayList<ArrayList<Integer>> permuteUnique (int[] num) {
         Arrays.sort(num);
        int[] v = new int[num.length];
        ArrayList<ArrayList<Integer>> result = new ArrayList<>();
        List<Integer> list = new ArrayList<>();

        Set<String> set = new HashSet<>();

        dfs(num, v, result, list, set);
        return result;
    }

    static public void dfs(int[] num, int[] v, ArrayList<ArrayList<Integer>> result,
                           List<Integer> list, Set<String> set ) {
        if (list.size() == num.length) {
            String join = getString(list);
            if (!set.contains(join)) {
                result.add(new ArrayList<>(list));
                set.add(join);
            }
            return;
        }
        for (int i = 0; i < num.length; i++) {
            if (v[i] == 0) {
                list.add(num[i]);
                v[i] = 1;
                dfs(num, v, result, list, set);
                list.remove(list.size() - 1);
                v[i] = 0;
            }
        }
    }

    static  public String getString (List<Integer> list) {
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < list.size(); i++) {
            sb.append(list.get(i) + "_");
        }
        return sb.toString();
    }
}