Leetcode 144. Binary Tree Preorder Traversal (Medium) (cpp)

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本文介绍LeetCode 144题——二叉树的前序遍历，提供了中等难度的C++实现方案。文章详细解释了递归方法，并附带完整的代码示例。

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Leetcode 144. Binary Tree Preorder Traversal (Medium) (cpp)

Tag: Tree, Stack

Difficulty: Medium

/*

144. Binary Tree Preorder Traversal (Medium)

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?

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