题解 | #没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>> permute (int[] num) {
        Arrays.sort(num);
        ArrayList<ArrayList<Integer>> res = new ArrayList<ArrayList<Integer>>();
        recursion(res, num, 0);
        return res;
    }
    public void swap(int[] num, int i, int j) {
        int temp = num[i];
        num[i] = num[j];
        num[j] = temp;
    }
    public void recursion(ArrayList<ArrayList<Integer>> res, int[] num, int x) {
        if (x == num.length - 1) {
            ArrayList<Integer> temp = new ArrayList<>();
            for (int i = 0; i < num.length; i++)
                temp.add(num[i]);
            res.add(temp);
        }
        for (int i = x; i < num.length; i++) {
            swap(num, i, x);
            recursion(res, num, x + 1);
            swap(num, i, x);
        }
    }
}