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

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
    vector<int> rst;
public:
    vector<int> preorderTraversal(TreeNode *root) {
        if(root){
            rst.push_back(root->val);
            preorderTraversal(root->left);
            preorderTraversal(root->right);
        }
        return rst;
    }
};