Q6: Binary Tree Preorder Traversal

问题描述

Given a binary tree, return the preorder traversal of its nodes‘ values.

For example:
Given binary tree {1,#,2,3},

   1
         2
    /
   3

return [1,2,3].

Note: Recursive solution is trivial, could you do it iteratively?

解决原理

递归

代码

 1 /**
 2  * Definition for binary tree
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution {
11     vector<int> rst;
12 public:
13     vector<int> preorderTraversal(TreeNode *root) {
14         if(root){
15             rst.push_back(root->val);
16             preorderTraversal(root->left);
17             preorderTraversal(root->right);
18         }
19         return rst;
20     }
21 };