Diagonal Sum In Binary Tree

/*Complete the function below
Node is as follows:
class Node{
    int data;
    Node left,right;
    Node(int d){
        data=d;
        left=right=null;
    }
}
*/
class Tree {
    public static ArrayList <Integer> diagonalSum(Node root) {
        int height = diagonalHeightUtil(root, 0);
        ArrayList<Integer> res = new ArrayList<> ();
        
        for(int i = 0; i < height; i++)
            res.add(0);
        
        diagonalSumUtil(root, 0, res); 
        return res;
    }
    
    private static int diagonalHeightUtil(Node root, int height) {
        if(root == null)
            return height;
        
        return Math.max(diagonalHeightUtil(root.left, height + 1), diagonalHeightUtil(root.right, height)); 
    }
    
    private static void diagonalSumUtil(Node root, int height, ArrayList<Integer> res) {
        if(root == null)
            return ;
        
        res.set(height, res.get(height) + root.data);
        
        diagonalSumUtil(root.right, height, res);
        diagonalSumUtil(root.left, height + 1, res);
    }
    
}