题目描述：
LeetCode 687. Longest Univalue Path
Given a binary tree, find the length of the longest path where each node in the path has the same value. This path may or may not pass through the root.
Note: The length of path between two nodes is represented by the number of edges between them.
Example 1:
Input:
5
/ \
4 5
/ \ \
1 1 5
Output:
2
Example 2:
Input:
1
/ \
4 5
/ \ \
4 4 5
Output:
2
Note: The given binary tree has not more than 10000 nodes. The height of the tree is not more than 1000.
题目大意：
给定二叉树，求节点值全部相等的最长路径。路径不一定要通过树根。
解题思路：
递归（Recursion）
Python代码：
# 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 longestUnivaluePath(self, root):
"""
:type root: TreeNode
:rtype: int
"""
if not root: return 0
left, right, val = root.left, root.right, root.val
return max(self.longestPath(left, val) + self.longestPath(right, val), \
self.longestUnivaluePath(left), \
self.longestUnivaluePath(right))
def longestPath(self, root, val):
if not root or root.val != val: return 0
return 1 + max(self.longestPath(root.left, val), self.longestPath(root.right, val))
本文链接：http://bookshadow.com/weblog/2017/10/01/leetcode-longest-univalue-path/
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