LeetCode_KthSmallestElementBST.py

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

class Solution(object):
    def kthSmallest(self, root, k):
        """
        :type root: TreeNode
        :type k: int
        :rtype: int
        """
        from collections import deque
        stack = deque()
        while root.left:
            stack.append(root)
            root = root.left
        return self.foo(root, k, stack)
        
        
    def foo(self, root, k, stack):
        print
        if k == 1:
            return root.val
        if root.right is not None:
            root = root.right
            stack.append(root)
            while root.left is not None:
                root = root.left
                stack.append(root)
        root = stack.pop()
        return self.foo(root, k-1, stack)