二叉树BST迭代器（非递归中序遍历）——Binary Search Tree Iterator

class BSTIterator:
    """
    @param: root: The root of binary tree.
    """
    def __init__(self, root):
        self.stack = []
        while root != None:
            self.stack.append(root)
            root = root.left

    """
    @return: True if there has next node, or false
    """
    def hasNext(self):
        return len(self.stack) > 0

    """
    @return: return next node
    """
    def next(self):
        node = self.stack.pop()
        cur = node.right
        while cur is not None:
            self.stack.append(cur)
            cur = cur.left
        return node