Java implementation LeetCode 687 with a maximum value of the path (recursive)

687. The value of the path with the longest

Given a binary tree, to find the longest paths, each node in this path have the same value. This path may or may not pass through the root node.

Note: the length of the path between two nodes is represented by the number of edges therebetween.

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 not more than 10,000 nodes. Height of the tree does not exceed 1000.

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    private int maxL = 0;
    
    public int longestUnivaluePath(TreeNode root) {
       
        if(root == null) return 0;
        getMaxL(root, root.val);
        return maxL;
    }
    
    private int getMaxL(TreeNode r, int val) {
        if(r == null) return 0;
        int left = getMaxL(r.left, r.val);
        int right = getMaxL(r.right, r.val);
        maxL = Math.max(maxL, left+right); // 路径长度为节点数减1所以此处不加1
        if(r.val == val) // 和父节点值相同才返回以当前节点所能构成的最长通知路径长度, 否则返回0
            return Math.max(left, right) + 1;
        return 0;
    }
}