30min

class Solution2:
    def __init__(self):
        self.res=None

    def lowestCommonAncestor(self, root: 'TreeNode', p: 'TreeNode', q: 'TreeNode') -> 'TreeNode':
        self.dfs(root,p,q)
        return self.res

    def dfs(self,root:TreeNode,p:TreeNode,q:TreeNode)->bool:
        if not root:return False
        left=1 if self.dfs(root.left,p,q) else 0
        right=1 if self.dfs(root.right,p,q) else 0
        mid=1 if root==p or root==q else 0
        if left+right+mid>1:self.res=root
        return left or right or mid  # 這里要有mid

有問題的寫法，函數(shù)功能寫得很亂

class Solution:
    def lowestCommonAncestor(self, root: 'TreeNode', p: 'TreeNode', q: 'TreeNode') -> 'TreeNode':
        if not root: return None
        if self.subTreeHasNode(root,p,q):return root
        left=self.lowestCommonAncestor(root.left,p,q)
        if left:return left
        right=self.lowestCommonAncestor(root.right,p,q)
        if right:return right

    def subTreeHasNode(self,root:TreeNode,p:TreeNode,q:TreeNode)->bool:
        if not root:return True
        mid=True if root==p or root==q else False
        left=self.subTreeHasNode(root.left,p,q)
        right=self.subTreeHasNode(root.right,p,q)
        if (mid and left)or (mid and right)or(left and right):return True #到底是含有一個(gè)節(jié)點(diǎn)？還是兩邊都有呢？