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.

/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
int re = 0;
public int longestUnivaluePath(TreeNode root) {
help(root, 0);
return re;
}

public int help(TreeNode root, int n) {
if (root == null)
return 0;
int left = help(root.left, root.val);
int right = help(root.right, root.val);
re = Math.max(re, left + right);
return root.val == n ? Math.max(left, right) + 1 : 0;
}
}