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
        ArrayList<ArrayList<Integer>> result = new ArrayList<>();
        Arrays.sort(num);  //从小到大排
        ArrayList<Integer> path = new ArrayList<>();
        boolean[] used = new boolean[num.length];

        //递归寻找每一次结果
        recursion(result, path, num, used);

        return result;
    }

    public void recursion(ArrayList<ArrayList<Integer>> result,
                        ArrayList<Integer> path, int[] num, boolean[] used) {
        //递归结束条件
        if (path.size() == num.length) {
            result.add(new ArrayList<>(path));
            return;
        }
        for (int i = 0; i < num.length; i++) {
            if (used[i]) continue;
            if (i > 0 && num[i] == num[i - 1] && !used[i - 1]) continue;
            if (!used[i]) {
                used[i] = true;
                path.add(num[i]);
                recursion(result, path, num, used);
                used[i] = false;
                path.remove(path.size() - 1);
            }
        }
    }
}