題目

https://leetcode.com/problems/lexicographical-numbers/

題解

思路：先序遍歷 10 叉樹，參考：Simple Java DFS Solution

The idea is pretty simple. If we look at the order we can find out we just keep adding digit from 0 to 9 to every digit and make it a tree. Then we visit every node in pre-order. 1 2 3 .../\ /\ /\10 ...19 20...29 30...39 .... class Solution {public List<Integer> lexicalOrder(int n) {ArrayList<Integer> res = new ArrayList<>();for (int i = 1; i < 10; i++) {dfs(i, n, res);}return res;}public void dfs(int num, int max, List<Integer> list) {if (num > max) return;list.add(num);for (int i = 0; i < 10; i++) {if (num * 10 + i > max) return;dfs(num * 10 + i, max, list);}} }

總結

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