Leetcode 173. Binary Search Tree Iterator

Inorder Traversal을 구현하면 되는 간단한 문제...인데 난이도가 midium으로 되어있어서 의외였던 문제

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class BSTIterator:

    def __init__(self, root: TreeNode):
        self.queue = collections.deque()
        
        def dfs(node):
            if not node: return
            
            dfs(node.left)
            self.queue.append(node.val)
            dfs(node.right)
        
        dfs(root)

    def next(self) -> int:
        """
        @return the next smallest number
        """
        return self.queue.popleft()

    def hasNext(self) -> bool:
        """
        @return whether we have a next smallest number
        """
        return len(self.queue)


# Your BSTIterator object will be instantiated and called as such:
# obj = BSTIterator(root)
# param_1 = obj.next()
# param_2 = obj.hasNext()

https://leetcode.com/problems/binary-search-tree-iterator/