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) {
        // write code here
        Arrays.sort(num);
        ArrayList<ArrayList<Integer>> ret = new ArrayList<ArrayList<Integer>>();
        boolean[] arr = new boolean[num.length];
        ArrayList<Integer> tmp = new ArrayList<Integer>();
        recursion(ret, num, tmp, arr);

        return ret;
    }

    public void recursion(ArrayList<ArrayList<Integer>> ret, int[] num, ArrayList<Integer> tmp, boolean[] arr) {
        if (num.length == tmp.size()) {
            ret.add(new ArrayList<Integer>(tmp));
            return;
        }
        for (int i = 0; i < num.length; i++) {
            if (arr[i]) {
                continue;
            }
            if (i > 0 && num[i] == num[i-1] && !arr[i-1]) {
                continue;
            }
            
            arr[i] = true;
            tmp.add(num[i]);
            recursion(ret, num, tmp, arr);
            arr[i] = false;
            tmp.remove(tmp.size() - 1);
        }

    }

}