298. Binary Tree Longest Consecutive Sequence

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    private int maxLength = 0;
    public int longestConsecutive(TreeNode root) {
      helper(root);
      
      return maxLength;
        
    }
    private int helper(TreeNode root){
      if(root == null){
        return 0;
      }
      
      int left = helper(root.left);
      int right = helper(root.right);
      
      if(root.left != null && root.left.val == root.val + 1){
        left = left + 1;
      }else{
        left = 1;
      }
      
      
      if(root.right != null && root.right.val == root.val + 1){
        right = right + 1;
      }else{
        right = 1;
      }
      
      int length = Math.max(left,right);
      maxLength = Math.max(length,maxLength);
      
      return length;
    }
}