2022.03.07 - NC038.BM55 没有重复项数字的全排列

1. 题目

2. 思路

(1) 回溯

• 利用回溯+交换元素实现全排列。

3. 代码

import java.util.ArrayList;

public class Test {
    public static void main(String[] args) {
    }
}

class Solution {
    public ArrayList<ArrayList<Integer>> permute(int[] num) {
        ArrayList<ArrayList<Integer>> res = new ArrayList<>();
        backtrack(num, 0, num.length, res);
        return res;
    }

    public void backtrack(int[] num, int index, int n, ArrayList<ArrayList<Integer>> res) {
        if (index == n) {
            ArrayList<Integer> list = new ArrayList<>();
            for (int i = 0; i < n; i++) {
                list.add(num[i]);
            }
            res.add(list);
            return;
        }
        for (int i = index; i < n; i++) {
            int temp = num[index];
            num[index] = num[i];
            num[i] = temp;
            backtrack(num, index + 1, n, res);
            temp = num[index];
            num[index] = num[i];
            num[i] = temp;
        }
    }
}