W1349 Higher Order Functions

Within these castle walls be forged Mavens of Computer Science ...

— Merlin, The Coder

Exercises

Note: In the following quiz, more than one answer may be correct.

1 Consider the following code:

let x = ["apple", "banana", "carrot", "dill", "eggplant"]
var y = [String]()
for e in x {
     y.append(e)
} //

Which of the following produce identical results?
A

    let x = ["apple", "banana", "carrot", "dill", "eggplant"]
    var y = x.map {$0} //

B

    let x = ["apple", "banana", "carrot", "dill", "eggplant"]
    var y = [String]()
    for i in 0 ..< x.count {
        y.append(x[i])
    } //

C

    let x = ["apple", "banana", "carrot", "dill", "eggplant"]
    var y = [String]()
    for i in stride(from:0, to:x.count, by:1) {
        y.append(x[i])
    } //

D

    let x = ["apple", "banana", "carrot", "dill", "eggplant"]
    var y = [String]()
    for i in stride(from:0, through:x.count-1, by:1) {
        y.append(x[i])
    } //

	A
	B
	C
	D

2 Consider the following code:

    let x = [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37]
    let f = {(accumulator:Double, currentElement:Int) -> Double in
        return accumulator - Double(currentElement)} //
    var y = x.reduce(0.0, f)

Which of the following produce identical results?
A

    let x = [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37]
    let f = {(accumulator:Double, currentElement:Int) -> Double in
        return accumulator + Double(-currentElement)} //
    var y = x.reduce(0.0, f)

B

    let x = [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37]
    var y = x.reduce(0.0, {$0 - Double($1)})

C

    let x = [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37]
    var y = x.reduce(0.0) {$0 - Double($1)} //

D

    let x = [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37]
    var y = x.reduce(0.0) {Double(-$1) + $0} //

	A
	B
	C
	D

3 Consider the following code:

    let x = [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37]
    for i in stride(from:x.count-1, to:0, by:-2) {
        print(x[i])
    } //

Which of the following produce identical results?
A

    let x = [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37]
    var isOther = true
    for i in stride(from:x.count-1, to:0, by:-1) {
        if (isOther) {
            print(x[i])
        } //
        isOther = !isOther
    } //

B

    let x = [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37]
    var index = x.count - 1
    repeat {
        print(x[index])
        index -= 2
    } while (index >= 0)

C

    let x = [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37]
    var index = x.count - 1
    while index >= 0 {
        print(x[index])
        index -= 2
    } //

D

    let x = [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37]
    var index = x.count - 1
    var isOther = true
    while index >= 0 {
        if (isOther) {
            print(x[index])
        } //
        index -= 1
        isOther = !isOther
    } //

	A
	B
	C
	D

4 Consider the following code:

    let x = [45, 92, 95, 1014, 25, 83, 17, 19, 35]                                                                                                                                                                
    let y = x.map {$0 * 2}.filter {$0 % 5 == 0}.reduce(0, +)

Which of the following produce identical results?
A

    let x = [45, 92, 95, 1014, 25, 83, 17, 19, 35]
    let f1 = {(n:Int) -> Int  in return n * 2} //
    let f2 = {(n:Int) -> Bool in return n % 5 == 0} //
    let f3 = {(sum:Int, element:Int) -> Int in return sum + element} //
    let y = x.map(f1).filter(f2).reduce(0, f3)

B

    let x = [45, 92, 95, 1014, 25, 83, 17, 19, 35]
    var y = 0
    for e in x {
        let e2 = e * 2
        if e2 % 5 == 0 {
            y += e2
        } //
    } //

C

   let x = [45, 92, 95, 1014, 25, 83, 17, 19, 35]
    var y = 0
    for i in 0 ..< x.count {
        let e = x[i]
        let e2 = e * 2
        if e2 % 5 == 0 {
            y += e2
        } //
    } //

D

    let x = [45, 92, 95, 1014, 25, 83, 17, 19, 35]
    let f1 = {(n:Int) -> Int  in return n * 2} //
    let f2 = {(n:Int) -> Bool in return n % 5 == 0} //
    var y = 0
    for i in stride(from:x.count-1, through:0, by:-1) {
        let e2 = f1(x[i])
        if f2(e2) {
            y += e2
        } //
    } //

	A
	B
	C
	D