有关二叉树的做题笔记，Python实现

二叉树的定义

# Definition for a binary tree node.
class TreeNode:
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None

236. 二叉树的最近公共祖先 Lowest Common Ancestor of a Binary Tree

LeetCodeCN 第236题链接

首先如果root为空，返回root，然后如果root就是p或者q，那root就是最近公共祖先。然后分别对左子树和右子树做递归并保存结果，如果两边都能找到，证明本节点就是最近公共祖先，如果一边找得到，一边找不到，则往能找到的那边继续找下去。

class Solution:
    def lowestCommonAncestor(self, root: 'TreeNode', p: 'TreeNode', q: 'TreeNode') -> 'TreeNode':
        if root is None:
            return None
        if root == p or root == q:
            return root
        left = self.lowestCommonAncestor(root.left, p, q)
        right = self.lowestCommonAncestor(root.right, p, q)
        if left or right:
            if left is None:
                return right
            elif right is None:
                return left
            else:
                return root
        else:
            return None

下一题：235. 二叉搜索树的最近公共祖先 Lowest Common Ancestor of a Binary Search Tree