LeetCode OJ - Binary Tree Preorder Traversal (C++) (try 2 times) (Recursive)

為了練習尋找實習時會碰到的問題，我用別人推薦的 LeetCode online judge。
希望能直接寫程式，不用事先編譯就能直接AC。
這是下面是我寫的 Binary Tree Preorder Traversal 的解法。

To practice future interview question, I use LeetCode online judge.
I am trying to type code directly on website without compile in other tool.
The following program is my Binary Tree Preorder Traversal solution.

編譯錯誤次數 Compile Error number: 0
嘗試次數 Try number: 2 (until first AC) (RE: 1)
是否事先在其他工具編譯 if compile first in other tool: No

使用的程式語言 using programming language: C++
以前是否看過 seen this problem before: Yes

RE原因: 使用vector時，用assign的方式，但是那時vector沒有實際大小，
改成push_back()就AC了~

點這裡看題目 Click here to see this Problem!

Recursive的版本實在太簡單了，這個是Iterative版本~(還是很簡單= =)

原本多寫了一個function來跑遞迴，上面的程式是兩個function。
後來改成用原本的遞迴就解決即可(下面的程式)。

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

view raw LeetCode OJ - Binary Tree Preorder Traversal (C++) (try 2 times) (Recursive)1.cpp hosted with ❤ by GitHub

	/**
	* Definition for binary tree
	* struct TreeNode {
	* int val;
	* TreeNode *left;
	* TreeNode *right;
	* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
	* };
	*/
	class Solution {
	private:
	vector<int> preOrder;
	public:
	vector<int> preorderTraversal(TreeNode *root) {
	if(root == NULL)
	return preOrder;//just return, no experssion would accept this vector
	preOrder.push_back(root -> val);
	preorderTraversal(root -> left);
	preorderTraversal(root -> right);
	return preOrder;
	}
	};

view raw LeetCode OJ - Binary Tree Preorder Traversal (C++) (try 2 times) (Recursive)2.cpp hosted with ❤ by GitHub

If you want to use (copy, paste or quote) my original article, please contact me through email. (autek.roy@gmail.com) If there is any mistake or comment, please let me know. :D

如要使用(複製貼上或轉載)作者原創文章， 請來信跟我聯絡。(autek.roy@gmail.com) 如果有發現任何的錯誤與建議請留言或跟我連絡。 : )

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