LeetCode Binary Tree Maximum Path Sum

 1 /**
 2  * Definition for binary tree
 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 int max = Integer.MIN_VALUE;
12     public int maxPathSum(TreeNode root) {
13         if (root == null) {
14             return 0;
15         }
16         maxSum(root);
17         return max;
18     }
19 
20     private int  maxSum(TreeNode root) {
21         if (root == null) {
22             return 0;
23         }
24         int leftSum=0;
25         int rightSum=0;
26         int val=root.val;
27         if (root.left != null) {
28             leftSum = maxSum(root.left);
29             if (leftSum > 0) {
30                 val = val + leftSum;
31             }
32         }
33 
34         if (root.right != null) {
35             rightSum = maxSum(root.right);
36             if (rightSum > 0) {
37                 val = val + rightSum;
38             }
39         }
40 
41         if (val > max) {
42             max = val;
43         }
44 
45         return Math.max(root.val, Math.max(root.val + leftSum, root.val + rightSum));
46 
47 
48     }
49 }