Interview Question 1

Interview Question 1

/* QUESTION:
In an unsorted array of negative and positive integers, write a function, hasSumOf3Ints(array, n), that returns true if you find three numbers in the array that add up to a passed number, "n". 

(ie. array of [3,10,2,-3,100,4,0,-103], and n=14, 10, 4, and 0 is found and thus it would return true)
*/

// Error enum created at the end to properly throw errors including a function message() to directly display the error in the catch

enum Errors: ErrorType {
    case EmptyArray
    case Unknown
    
    func message() -> String {
        switch self {
        case .EmptyArray:
            return "Array seems to be empty"
        case .Unknown:
            return "Unknown error"
        }
    }
}

let array = [3,10,2,-3,100,4,0,-103]

// To simplify things we started with a sum of 2

func hasSumOf2Ints(array: [Int], n: Int) -> Bool {
    
    guard array.count != 0 else { return false }
    
    for (index, element) in array.enumerate() {
        
        var array2 = array
        array2.removeAtIndex(index)
        
        for secondElement in array2 {
            
            let sum = element + secondElement
            
            if sum == n {
                
                return true
            }
        }
    }
    
    return false
}

print(hasSumOf2Ints(array, n: 16))

// Used the above to do a more complex sum of 3

func hasSumOf3Ints(array: [Int], n: Int) throws -> Bool {
    
    guard array.count != 0 else { throw Errors.EmptyArray }
    
    let sortedArray = array.sort()
    
    for (index, element) in sortedArray.enumerate() {
        
        print("index", index)
        print("element", element)
        
        var first = index + 1
        var last = sortedArray.count - 1
        
        while first < last {
            
            let sum = element + sortedArray[first] + sortedArray[last]
            print("sum", sum)
            print("first", first)
            print("last", last)
            
            if sum == n {
                return true
            }
            
            if sum > n {
                last -= 1
            } else if sum < n {
                first += 1
            }
        }
    }
    
    return false
}

do {
    print(try hasSumOf3Ints(arrayUnsorted, n: 16))
} catch {
    if let error = error as? Errors {
        print(error.message())
    }
}