LC_606

今天是一道先序遍历二叉树的题目

先看题目

 

 递归的思路比较简单，先考虑使用递归的方法解题

方法1：递归

 1 /**
 2  * Definition for a binary tree node.
 3  * public class TreeNode {
 4  *     int val;
 5  *     TreeNode left;
 6  *     TreeNode right;
 7  *     TreeNode() {}
 8  *     TreeNode(int val) { this.val = val; }
 9  *     TreeNode(int val, TreeNode left, TreeNode right) {
10  *         this.val = val;
11  *         this.left = left;
12  *         this.right = right;
13  *     }
14  * }
15  */
16 class Solution {
17     public String ret = "";
18     public String tree2str(TreeNode root) {
19         pre(root);
20         return ret.substring(0,ret.length() - 1);
21     }
22     public void pre(TreeNode root){
23         if(root != null){
24             ret += String.valueOf(root.val);
25         }
26         
27         if(root.left != null){
28             ret += "(";
29             pre(root.left);
30         }else if(root.right != null){
31             ret += "()";
32         }
33         if(root.right != null){
34             ret += "(";
35             pre(root.right);
36         }
37         ret += ")";
38     }
39 }

 

方法2 迭代模拟递归

posted @ 2022-03-19 09:23  雨下_整夜  阅读(23)  评论(0)  编辑  收藏  举报