给定一个二叉树, 找到该树中两个指定节点的最近公共祖先。
百度百科中最近公共祖先的定义为：“对于有根树 T 的两个结点 p、q，最近公共祖先表示为一个结点 x，满足 x 是 p、q 的祖先且 x 的深度尽可能大（一个节点也可以是它自己的祖先）。”
# Definition for a binary tree node.
# class TreeNode:
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
class Solution:
def lowestCommonAncestor(self, root: TreeNode, p: TreeNode, q: TreeNode) -> TreeNode:
if root is None:
return None
if root == p:
return p
if root == q:
return q
"""
如果root是null，则说明我们已经找到最底了，返回null表示没找到
如果root与p相等或者与q相等，则返回root
如果左子树没找到，递归函数返回null，证明p和q同在root的右侧，那么最终的公共祖先就是右子树找到的结点
如果右子树没找到，递归函数返回null，证明p和q同在root的左侧，那么最终的公共祖先就是左子树找到的结点
"""
L = self.lowestCommonAncestor(root.left,p,q)
R = self.lowestCommonAncestor(root.right,p,q)
if L and R:
return root
return L if L else R
class Solution:
def lowestCommonAncestor(self, root: 'TreeNode', p: 'TreeNode', q: 'TreeNode') -> 'TreeNode':
has_p,has_q,ancestor = self.solver(root,p,q)
return ancestor
def solver(self,root,p,q):
if root is None:
return False,False,None
has_p_left,has_q_left,ancestor_left = self.solver(root.left,p,q)
has_p_right,has_q_right,ancestor_right = self.solver(root.right,p,q)
if has_p_left is True or has_p_right is True or root.val == p.val:
has_p = True
else:
has_p = False
if has_q_left is True or has_q_right is True or root.val == q.val:
has_q = True
else:
has_q = False
if ancestor_left is not None:
ancestor = ancestor_left
elif ancestor_right is not None:
ancestor = ancestor_right
elif ancestor_left is None and ancestor_right is None:
if has_p is True and has_q is True:
ancestor = root
else:
ancestor = None
return has_p,has_q,ancestor