binary-search-tree-iterator.py

# 173. Binary Search Tree Iterators
# https://leetcode.com/problems/binary-search-tree-iterator/

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

class BSTIterator:

    def __init__(self, root: TreeNode):
        self.stack = []
        self._left_most_node(root)
    
    def _left_most_node(self, node: TreeNode):
        while node is not None:
            self.stack.append(node)
            node = node.left

    def next(self) -> int:
        """
        @return the next smallest number
        """
        aux = self.stack.pop()
        if aux.right is not None:
            self._left_most_node(aux.right)
        return aux.val

    def hasNext(self) -> bool:
        """
        @return whether we have a next smallest number
        """
        return len(self.stack) > 0
        


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