Swift Online Test

Change the Readable protocol and the ReadableObject and ReadOnceObject classes, so that:

• ReadableObject and ReadOnceObject implement the Readable protocol.
• When the read method is called on the ReadableObject class, it returns the value that it received in the constructor.
• When the read method is called on the ReadOnceObject class it returns the value that it received in the constructor the first time it’s called and returns an empty string every other time.
• The isReadable method returns true in the ReadableObject class. The isReadable method of the ReadOnceObject class should return true the first time read is called, and false every other time.

An application uses the User and Subscription classes for tracking all subscriptions that a user has purchased. Currently, the memory occupied by instances of those classes is never reclaimed.

Without changing the public API, fix the memory leak.

Write a function that when passed an array and a target sum, returns, efficiently with respect to time used, two distinct zero-based indices of any two of the numbers whose sum is equal to the target sum. If there are no two numbers, the function should return nil.

For example, findTwoSum([ 3, 1, 5, 7, 5, 9 ], 10) should return a single dimensional array with two elements and contain any of the following pairs of indices:

• 0 and 3 (or 3 and 0) as 3 + 7 = 10
• 1 and 5 (or 5 and 1) as 1 + 9 = 10
• 2 and 4 (or 4 and 2) as 5 + 5 = 10

Consider the following Swift definition of the structure Car:

struct Car {
    var color:UIColor?
    let model:String
    
    init(model:String) {
        self.model = model
        self.color = nil
    }

    mutating func changeColor(color:UIColor) {
        self.color = color
    }
}

Select the statements that are correct.