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.

题目含义：找出二叉树中，最长的链路长度（由相同值构成的链路，可以不包含根节点）

    private int sameNodeValue(TreeNode node, int[] res) {
        int l = node.left != null ? sameNodeValue(node.left, res) : 0;
        int r = node.right != null ? sameNodeValue(node.right, res) : 0;
        int resl = node.left != null && node.left.val == node.val ? l + 1 : 0;
        int resr = node.right != null && node.right.val == node.val ? r + 1 : 0;
        res[0] = Math.max(res[0], resl + resr);
        return Math.max(resl, resr);
    }    
    
    public int longestUnivaluePath(TreeNode root) {
        int[] res = new int[1];
        if (root != null) sameNodeValue(root, res);
        return res[0];        
    }