Leetcode练习(Python)：栈类：第173题：二叉搜索树迭代器：实现一个二叉搜索树迭代器。你将使用二叉搜索树的根节点初始化迭代器。 调用 next() 将返回二叉搜索树中的下一个最小的数。

# 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.result = []
        if root:
            self.inorder(root)

    def inorder(self, node):
        if node.left:
            self.inorder(node.left)
        self.result.append(node.val)
        if node.right:
            self.inorder(node.right)

    def next(self) -> int:
        """
        @return the next smallest number
        """
        if self.result:
            return self.result.pop(0)

    def hasNext(self) -> bool:
        """
        @return whether we have a next smallest number
        """
        if len(self.result) > 0:
            return True
        else:
            return False

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