You have a method named GetCustomerIDs that returns a list of integers. Each entry in the list represents a customer ID that is retrieved from a list named Customers. The Customers list contains 1,000 rows.
Another developer creates a method named ValidateCustomer that accepts an integer parameter and returns a Boolean value. ValidateCustomer returns true if the integer provided references a valid customer.
ValidateCustomer can take up to one second to run.
You need to create a method that returns a list of valid customer IDs. The code must execute in the shortest amount of time.
What should you do? (Develop the solution by selecting and ordering the required code snippets. You may not need all of the code snippets.)