/* Preorder traversal
   The idea is to do a preorder traversal of the tree.
   In the preorder traversal, keep track of the value calculated till the current node, let this value be val.
   For every node, we update the val as val10 plus node’s data.
*/
var sumNumberUtil = function(node, val) {
    if (!node) {
        return 0;
    }
    else {
        val = val * 10 + node.val;

        if (!node.left && !node.right)
        {
            return val;
        }
        else {
            return sumNumberUtil(node.left, val) + sumNumberUtil(node.right, val);
        }
    }
}

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number}
 */
var sumNumbers = function(root) {
    return sumNumberUtil(root, 0);
};