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 {
    int maxLength = 0;
    public int longestConsecutive(TreeNode root) {
        dfs(root, null, 0);
        return maxLength;
    }
    
    private void dfs(TreeNode node, TreeNode parent, int curLength) {
        if (node == null) {
            return;
        }
        curLength = (parent != null && node.val == parent.val + 1) ? curLength + 1 : 1;
        maxLength = Math.max(curLength, maxLength);
        dfs(node.left, node, curLength);
        dfs(node.right, node, curLength);
    }
}