Binary Tree Maximum Path Sum

    public int maxPathSum(TreeNode root) {
        // Start typing your Java solution below
        // DO NOT write main() function
        ArrayList<Integer> result = new ArrayList<Integer>(1);
        result.add(Integer.MIN_VALUE);
        maxPathSum(root, result);
        return result.get(0);
    }
    
    public int maxPathSum(TreeNode root, ArrayList<Integer> result) {
        if(root == null) return 0;
        int left = maxPathSum(root.left, result);
        int right = maxPathSum(root.right, result);
        int max = root.val;
        if(left > 0) max += left;
        if(right > 0) max += right;
        if(result.get(0) < max) result.set(0, max);
        return Math.max(root.val, Math.max(left, right) + root.val);
    }