687. Longest Univalue Path

题目

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.

解题思路

见程序注释