62.二叉搜索树的第k个节点(python)

题目描述

给定一棵二叉搜索树，请找出其中的第k小的结点。例如， （5，3，7，2，4，6，8）    中，按结点数值大小顺序第三小结点的值为4。

 

思路：中序遍历

class Solution:
    # 返回对应节点TreeNode
    def KthNode(self, pRoot, k):
        # write code here
        stack = []
        while stack or pRoot:
            if pRoot:
                stack.append(pRoot)
                pRoot = pRoot.left
            else:
                pRoot=stack.pop()
                k-=1
                if k == 0:
                    return pRoot
                pRoot=pRoot.right

2019-12-31 21:26:57

class Solution:
    # 返回对应节点TreeNode
    def KthNode(self, pRoot, k):
        # write code here
        def preorder(pRoot):
            if pRoot == None:
                return []
            return preorder(pRoot.left)+[pRoot]+preorder(pRoot.right)
        res = preorder(pRoot)
        if len(res)<k or k < 1:
            return None
        return res[k-1]

递归版

class Solution:
    # 返回对应节点TreeNode
    def __init__(self):
        self.count=0
    def KthNode(self, pRoot, k):
        # write code here
        if pRoot == None:
            return None
        node = self.KthNode(pRoot.left,k)
        if node:
            return node
        self.count += 1
        if self.count == k:
            return pRoot
        node = self.KthNode(pRoot.right,k)
        if node:
            return node