sum-each-group.kt

// prepare variable employees which is a list of Employee object
// Same as Task 0
employees.groupBy { it.department }
    .map { group ->
        val departmentName = group.key
        val departmentEmployees = group.value
        val departmentTotalSalary = departmentEmployees.sumBy { it.salary }
        println("Total salary for department $departmentName is $departmentTotalSalary")
    }