Root to leaf paths sum

class Tree {
    int data;
    Tree left, right;

    Tree(int d) {
        data = d;
        left = null;
        right = null;
    }
}

class Solution {
    public static int treePathsSum(Node root) {
        return dfs(root, 0);
    }

    private static int dfs(Node node, int val) {
        if (node == null)
            return 0;

        val = val * 10 + node.data;
        if (node.left == null && node.right == null)
            return val;

        return dfs(node.left, val) + dfs(node.right, val);
    }
}