173.binary-search-tree-iterator.py

#
# @lc app=leetcode id=173 lang=python
#
# [173] Binary Search Tree Iterator
#

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

class BSTIterator(object):

    def __init__(self, root):
        """
        :type root: TreeNode
        """
        self.stack = []
        while root:
            self.stack.append(root)
            root = root.left
        

    def next(self):
        """
        @return the next smallest number
        :rtype: int
        """
        node = self.stack.pop()
        val = node.val
        if node.right:
            node = node.right
            while node:
                self.stack.append(node)
                node = node.left
        return val

    def hasNext(self):
        """
        @return whether we have a next smallest number
        :rtype: bool
        """
        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()
# @lc code=end