Two Sum

twoSum.swift

/**
* TwoSum
* Write a function that takes a list and outputs alist of numbers
* belonging to the list that can be summed up to the first element of the list.
*
* Test Cases
* > twoSum [17, 4, 5, 6, 10, 11, 4, -3, -5, 3, 15, 2, 7]
* 6, 11, 10, 7, 15, 2
*
* > twoSum [7, 6, 4, 1, 7, -2, 3, 12]
* 6, 1, 4, 3
*/

func twoSum(_ array: [Int]) -> [Int] {
    var result: [Int] = []
    var complement: [Int] = []
    let firstElement = array[0]
    
    for element in array {
        if complement.contains(element) {
            result.append(firstElement - element)
            result.append(element)
        } else {
            complement.append(firstElement - element)
        }
    }
    
    return result
}


func coolTwoSum(_ array: [Int])  -> [Int] {
    let firstElement = array[0]
    return array.filter { array.contains(firstElement - $0) }
}