Leetcode: Binary Tree Longest Consecutive Sequence

Given a binary tree, find the length of the longest consecutive sequence path.

The path refers to any sequence of nodes from some starting node to any node in the tree along the parent-child connections. The longest consecutive path need to be from parent to child (cannot be the reverse).

For example,
   1
         3
    /    2   4
                 5
Longest consecutive sequence path is 3-4-5, so return 3.
   2
         3
    / 
   2    
  / 
 1
Longest consecutive sequence path is 2-3,not3-2-1, so return 2.

 1 /**
 2  * Definition for a binary tree node.
 3  * public class TreeNode {
 4  *     int val;
 5  *     TreeNode left;
 6  *     TreeNode right;
 7  *     TreeNode(int x) { val = x; }
 8  * }
 9  */
10 public class Solution {
11     public int longestConsecutive(TreeNode root) {
12         if (root == null) return 0;
13         return helper(root, 0, Integer.MAX_VALUE);
14     }
15     
16     public int helper(TreeNode cur, int curLen, int preVal) {
17         curLen = (cur.val == preVal+1)? curLen+1 : 1;
18         int left=0, right=0;
19         if (cur.left != null) 
20             left = helper(cur.left, curLen, cur.val);
21         if (cur.right != null)
22             right = helper(cur.right, curLen, cur.val);
23         return Math.max(curLen, Math.max(left, right));
24     }
25 }

 1 /**
 2  * Definition for a binary tree node.
 3  * public class TreeNode {
 4  *     int val;
 5  *     TreeNode left;
 6  *     TreeNode right;
 7  *     TreeNode(int x) { val = x; }
 8  * }
 9  */
10 public class Solution {
11     ArrayList<Integer> res = new ArrayList<Integer>();
12     
13     public int longestConsecutive(TreeNode root) {
14         if (root == null) return 0;
15         res.add(0);
16         helper(root, 1);
17         return res.get(0);
18     }
19     
20     public void helper(TreeNode root, int curLen) {
21         if (curLen > res.get(0)) res.set(0, curLen);
22         if (root.left != null) {
23             int left = (root.left.val==root.val+1)? curLen+1 : 1;
24             helper(root.left, left);
25         }
26         if (root.right != null) {
27             int right = (root.right.val==root.val+1)? curLen+1 : 1;
28             helper(root.right, right);
29         }
30     }
31 }

 1 public class Solution {
 2     int res = 0;
 3     
 4     public int longestConsecutive(TreeNode root) {
 5         if (root == null) return 0;
 6         helper(root, 1);
 7         return res;
 8     }
 9     
10     public void helper(TreeNode root, int curLen) {
11         if (curLen > res) res = curLen;
12         if (root.left != null) {
13             int left = (root.left.val==root.val+1)? curLen+1 : 1;
14             helper(root.left, left);
15         }
16         if (root.right != null) {
17             int right = (root.right.val==root.val+1)? curLen+1 : 1;
18             helper(root.right, right);
19         }
20     }
21 }