Binary Tree Maximum Path Sum

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public int maxPathSum(TreeNode root) {
        ArrayList<Integer> maxSum = new ArrayList<Integer>(1);
        maxSum.add(Integer.MIN_VALUE);
        getMaxSum(root,maxSum);
        return maxSum.get(0);
    }

    public int getMaxSum(TreeNode root,ArrayList<Integer> maxSum){
        if(root==null){
            return 0;
        }
    
        int leftSum=0,rightSum=0;
        leftSum = getMaxSum(root.left,maxSum);
        rightSum = getMaxSum(root.right,maxSum);
    
        int curSum = Math.max(root.val,Math.max(root.val+leftSum,root.val+rightSum));
        maxSum.add(0,Math.max(maxSum.get(0), Math.max(curSum,root.val+leftSum+rightSum)));
        return curSum;
    }
}