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

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

}