1using System;
2using System.Collections.Generic;
3
4public class LexicalOrderDFS {
5    public void DFS(int current, int n, IList<int> result) {
6        if (current > n) return;
7        result.Add(current);
8        for (int i = 0; i <= 9; ++i) {
9            if (current * 10 + i > n) return;
10            DFS(current * 10 + i, n, result);
11        }
12    }
13
14    public IList<int> LexicalOrder(int n) {
15        IList<int> result = new List<int>();
16        for (int i = 1; i < 10; ++i) {
17            DFS(i, n, result);
18        }
19        return result;
20    }
21
22    public static void Main(string[] args) {
23        LexicalOrderDFS obj = new LexicalOrderDFS();
24        int n = 13;
25        IList<int> result = obj.LexicalOrder(n);
26        foreach (int num in result) {
27            Console.Write(num + " ");
28        }
29    }
30}

1