leetcode-236题:lowest common ancestor of a binary tree

题目

Given a binary tree, find the lowest common ancestor (LCA) of two given nodes in the tree.

思路

分别求出跟节点到p,q的路径,那么路径的共同前缀的末尾即为所求。

代码

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
# Definition for a binary tree node.
# class TreeNode(object):
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None

class Solution(object):

def visit(self, root, cur_path, pathes, p, q):
if root == None:
return
cur_path.append(root)
if root==p:
pathes.append(cur_path[:])
if root==q:
pathes.append(cur_path[:])
self.visit(root.left, cur_path, pathes, p, q)
self.visit(root.right, cur_path, pathes, p, q)
cur_path.pop()

def lowestCommonAncestor(self, root, p, q):
"""
:type root: TreeNode
:type p: TreeNode
:type q: TreeNode
:rtype: TreeNode
"""
if root == None:
return None
pathes = []
self.visit(root, [], pathes, p, q)
i = 0
while i < min(len(pathes[0]),len(pathes[1])):
if pathes[0][i] != pathes[1][i]:
break
i += 1
return pathes[0][i-1]