Binary Tree Maximum Path Sum

 1 public class Solution {
 2     public int maxPathSum(TreeNode root) {
 3         int res []={Integer.MIN_VALUE};
 4         helper(root,res);
 5         return res[0];
 6     }
 7     public int helper(TreeNode root,int[] res){
 8         if(root==null) return 0;
 9         int left = helper(root.left,res);
10         int right = helper(root.right,res);
11         int across = root.val+left+right;
12         int single = Math.max(root.val,Math.max(root.val+right,root.val+left));
13         res[0] = Math.max(res[0],Math.max(across,single));
14         return single;
15     }
16 }