173. Binary Search Tree Iterator (Medium) - TengnanYao/daily_leetcode GitHub Wiki

# 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: Optional[TreeNode]):
        self.arr = []
        self.i = -1
        def dfs(root):
            if root:
                dfs(root.left)
                self.arr.append(root.val)
                dfs(root.right)
        dfs(root)

    def next(self) -> int:
        self.i += 1
        if self.i < len(self.arr):
            return self.arr[self.i]
        return False

    def hasNext(self) -> bool:
        return self.i + 1 < len(self.arr)

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