Function dfs

javascript/0129-sum-root-to-leaf-numbers.js:18–27

(node, num)

var sumNumbers = function (root) {
    let total = 0;
    const dfs = (node, num) => {
        if (!node.left && !node.right) {
            num = num + node.val;
            total += +num;
            return;
        }

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

    dfs(root, '');
    return total;