class BSTIterator(object):

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

    def next(self):
        cur = self.stack.pop()
        node = cur.right
        while node:
            self.stack.append(node)
            node = node.left
        return cur.val

    def hasNext(self):
        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()

栈，中等，每日一题

展开二叉树的想法很简单，但是不符合代码“迭代器不修改源数据”的规范。

其实就是模拟一个中序遍历的过程

https://leetcode-cn.com/problems/binary-search-tree-iterator/

题解：https://leetcode-cn.com/problems/binary-search-tree-iterator/solution/fu-xue-ming-zhu-dan-diao-zhan-die-dai-la-dkrm/