Extract string values

extract_string_from_runes.go

func getProduct(digits string) (product int64, e error) {
	product = 1
	for _, digit := range digits {
		d, err := strconv.Atoi(string(digit))
		if err != nil {
			return -1, fmt.Errorf("cannot convert %v to int", digit)
		}
		product *= int64(d)
	}
	return product, nil
}



for i := 0; i <= len(digits)-span; i++ {
		product, err := getProduct(digits[i : i+span])
		if err != nil {
			return -1, err
		}
		if product > largestProduct {
			largestProduct = product
		}
	}