173. 二叉搜索树迭代器

# 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=[]
        self.index=0
        queue=[root]
        if not root:
            self.length=0
            return 
        a=lambda root: [] if not root else a(root.left)+[root.val]+a(root.right)
        # 中序遍历获得已经排序好的list
        self.result=a(root)
        self.length=len(self.result)

    def next(self) -> int:
        """
        @return the next smallest number
        """
        self.index+=1
        return self.result[self.index-1]


    def hasNext(self) -> bool:
        """
        @return whether we have a next smallest number
        """
        return self.index<=self.length-1



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