题解 | 火车进站

#牛客创作赏金赛# #刷题我是认真的#

解题思路：

1. 这个题有点不好搞，直接抄的别人的答案
2. 主要需要使用dfs 和回溯

import java.util.*;

public class Main {
    public static List<String> res = new ArrayList<>();

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int[] nums = new int[n];
        Stack<Integer> stk = new Stack<>();
        for (int i = 0; i < n; i++) {
            nums[i] = in.nextInt();
        }
        helper(nums, 0, stk, "", 0);
        Collections.sort(res);
        for (String s : res) {
            System.out.println(s);
        }
    }
    // 
    public static void helper(int[] nums, int i, Stack<Integer> stk, String s,
                              int n) {
        if (n == nums.length)
            res.add(s);
        if (!stk.empty()) {
            int tmp = stk.pop();
            helper(nums, i, stk, s + tmp + " ", n + 1);
            stk.push(tmp);
        }
        if (i < nums.length) {
            stk.push(nums[i]);
            helper(nums, i + 1, stk, s, n);
            stk.pop();
        }
    }
}