173

# 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):
        self.stack=[ ]
        while root:
            self.stack.append(root)
            root=root.left
    def hasNext(self):
        """
        :rtype: bool
        """
        return self.stack!=[ ]
    def next(self):
        """
        :rtype: int
        """
        p=self.stack.pop( )
        res=p.val
        p=p.right
        while p:
            self.stack.append(p)
            p=p.left
        return res
        
        

# Your BSTIterator will be called like this:
# i, v = BSTIterator(root), []
# while i.hasNext(): v.append(i.next())