687. Longest Univalue Path

              5
             / \
            4   5
           / \   \
          1   1   5

              1
             / \
            4   5
           / \   \
          4   4   5

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    int length;
    
    public int longestUnivaluePath(TreeNode root) {
        if(root == null){
            return 0;
        }
        
        length = 0;
        findLength(root);
        
        return length;
    }
    
    public int findLength(TreeNode node){
        if(node == null){
            return 0;
        }
        
        int left = findLength(node.left);
        int right = findLength(node.right);
        
        int currLeft = 0;
        int currRight = 0;
        
        if(node.left != null && node.left.val == node.val){
            currLeft = left + 1;
        }
        
        if(node.right != null && node.right.val == node.val){
            currRight = right + 1;
        }
        
        if(length < currLeft + currRight){
            length = currLeft + currRight;
        }
        
        return Math.max(currLeft, currRight);
    }
}

[문제] https://leetcode.com/problems/longest-univalue-path/