[LeetCode] 173. Binary Search Tree Iterator

轉自LeetCode

Implement an iterator over a binary search tree (BST). Your iterator will be initialized with the root node of a BST.

Calling next() will return the next smallest number in the BST.

Note: next() and hasNext() should run in average O(1) time and uses O(h) memory, where h is the height of the tree.

<Solution>
這題的概念就是要做一個 in-order 輸出的 iterator

這邊使用一個 stack 來輔助

code 如下(參考資料)