gistfile1.swift

var data1 = [1, 4, 7]
var data2 = [123, -2, 477, 3, 14, 6551]

/*
 * Write a recursive function which loops over the list adding the first element
 * to all remaining elements
 * until there is only 1 element remaining which is then returned
 */

func doStuff(input: [Int]) -> Int {
    // helper function takes an array, extracts first element and
    // adds it to remaining elements, returns the resulting array
    func removeFirstAndAddToOthers(elements: [Int]) -> [Int] {
        var remaining = elements
        let toAdd = remaining.removeAtIndex(0)
        return remaining.map({ element in element + toAdd})
    }

    switch input.count {
    case 0: return 0
    case 1: return input[0]                                     // return the last remaining element
    default: return doStuff(removeFirstAndAddToOthers(input))   // count > 1, call the function again
    }
}

println("The expected answer for data1 is 13"           // The expected answer for data1 is 13
println("Your answer is \(doStuff(data1))")             // Your answer is 13
println("Your answer for data2 is \(doStuff(data2))")   // Your answer for data2 is 10431