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.

題目含義：找出二叉樹中，最長的鏈路長度（由相同值構成的鏈路，可以不包含根節點）

 1     private int sameNodeValue(TreeNode node, int
 
[] res) {
 2         int l = node.left != null ? sameNodeValue(node.left, res) : 0;
 3         int r = node.right != null ? sameNodeValue(node.right, res) : 0;
 4         int resl = node.left != null && node.left.val == node.val ? l + 1 : 0;
 5         int resr = node.right != null && node.right.val == node.val ? r + 1 : 0;
 
 6         res[0] = Math.max(res[0], resl + resr);
 7         return Math.max(resl, resr);
 8     }    
 9     
10     public int longestUnivaluePath(TreeNode root) {
11         int[] res = new int[1];
12         if (root != null) sameNodeValue(root, res);
13         return res[0];        
14     }

687. Longest Univalue Path