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/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
 
public class Solution {
    public int maxPathSum(TreeNode root) {
        int[] maxSum = new int[] {Integer.MIN_VALUE};
        helper(root, maxSum);
        return maxSum[0];
    }
    private int helper(TreeNode root, int[] maxSum) {
        if(root == null) return 0;
        
        int left = Math.max(helper(root.left, maxSum), 0);
        int right = Math.max(helper(root.right, maxSum), 0);
        
        maxSum[0] = Math.max(maxSum[0], left + root.val + right);
        
        return root.val + Math.max(left, right);
    }
}