687.py

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    result: int = 0

    def longestUnivaluePath(self, root: TreeNode) -> int:

        def dfs(node: TreeNode) -> int:
            if node is None:
                return 0

            left = dfs(node.left)
            right = dfs(node.right)

            if node.left and node.val == node.left.val:
                left += 1
            else:
                left = 0

            if node.right and node.val == node.right.val:
                right += 1
            else:
                right = 0

            self.result = max(self.result, left + right)

            return max(left, right)

        dfs(root)
        return self.result