To prove safety offer - binary search tree node of the k small

Title Description

Given a binary search tree, please find the first k smaller nodes therein. For example, (5,3,7,2,4,6,8), the numerical values ​​according to the third junction point is 4 summary.

Thinking

In fact, the traversal sequence, the k-th node traversed

# -*- coding:utf-8 -*-
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
class Solution:
    def KthNode(self, root, k):
        #相当于中序遍历，遍历到的第k个点
        if k<=0 or not root:
            return None
        
        index = 0
        nodes = []
        while 1:
            while 1:
                while root.left:
                    nodes.append(root)
                    root = root.left
                index += 1
                if index == k:
                    return root
                if root.right:
                    root = root.right
                else:
                    break
            if len(nodes)>0:
                root = nodes.pop()
                index += 1
                if index == k:
                    return root
                while root.right == None and len(nodes)>0:
                    root = nodes.pop()
                    index += 1
                    if index == k:
                        return root
                if root.right:
                    root = root.right
                else:
                    break
            else:
                break
        return None