Leetcode 687. 最长同值路径

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

class Solution:
    def longestUnivaluePath(self, root: TreeNode) -> int:
        self.ret=0
        def path(node):
            if not node:
                return 0
            l=path(node.left)
            r=path(node.right)
            l=l if node.left and node.left.val==node.val else 0
            r=r if node.right and node.right.val==node.val else 0            
            self.ret=max(l+r,self.ret)
            return max(l,r)+1
        path(root)
        return self.ret