LeetCode OJ - Binary Tree Preorder Traversal (C++) (try 3 times) (Iterative)

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.

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.