Use a function to find common elements in two sequences in Swift

Question

I\'m trying to complete the exercise on page 46 of Apple\'s new book \"The Swift Programming Language\". It gives the following code:

func anyCommonElements         


        

Answer 1

The accepted answer is no longer valid for the latest version of Swift. Here is an update that is compatible with version 3.0.1, they have simplified how to make a generic array.

func showCommonElements<T: Sequence, U: Sequence>(_ lhs: T, _ rhs: U) -> [T.Iterator.Element]
    where T.Iterator.Element: Equatable, T.Iterator.Element == U.Iterator.Element {
        var result:[T.Iterator.Element] = []
        for lhsItem in lhs {
            for rhsItem in rhs {
                if lhsItem == rhsItem {
                    result.append(lhsItem)
                }
            }
        }
        return result
}

You can test the code with the following commands:

showCommonElements([1, 2, 3, 4, 5], [4, 7, 3])
showCommonElements(["apple", "banana", "orange", "peach"], ["orange", "pear", "apple"])

Answer 2

The cleanest way to solve this in Swift 3 is using the filter function as follows:

func anyCommonElements<T: Sequence, U: Sequence>(_ lhs: T, _ rhs: U) -> [T.Iterator.Element]
    where T.Iterator.Element: Equatable, T.Iterator.Element == U.Iterator.Element {
        return lhs.filter { rhs.contains($0) }
}