Published at Apr 14 2020
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Instructions

Test suite

Solution

Given a number from 0 to 999,999,999,999, spell out that number in English.

Handle the basic case of 0 through 99.

If the input to the program is `22`

, then the output should be
`'twenty-two'`

.

Your program should complain loudly if given a number outside the blessed range.

Some good test cases for this program are:

- 0
- 14
- 50
- 98
- -1
- 100

If you're on a Mac, shell out to Mac OS X's `say`

program to talk out
loud.

Implement breaking a number up into chunks of thousands.

So `1234567890`

should yield a list like 1, 234, 567, and 890, while the
far simpler `1000`

should yield just 1 and 0.

The program must also report any values that are out of range.

Now handle inserting the appropriate scale word between those chunks.

So `1234567890`

should yield `'1 billion 234 million 567 thousand 890'`

The program must also report any values that are out of range. It's fine to stop at "trillion".

Put it all together to get nothing but plain English.

`12345`

should give `twelve thousand three hundred forty-five`

.

The program must also report any values that are out of range.

Use *and* (correctly) when spelling out the number in English:

- 14 becomes "fourteen".
- 100 becomes "one hundred".
- 120 becomes "one hundred and twenty".
- 1002 becomes "one thousand and two".
- 1323 becomes "one thousand three hundred and twenty-three".

Go through the project setup instructions for Xcode using Swift:

http://exercism.io/languages/swift

http://exercism.io/languages/swift/tests

Notably from the source directory:

`swift test`

runs tests

`swift package generate-xcodeproj`

creates an Xcode project

A variation on JavaRanch CattleDrive, exercise 4a http://www.javaranch.com/say.jsp

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

```
import XCTest
@testable import SayTests
XCTMain([
testCase(SayTests.allTests),
])
```

```
import XCTest
@testable import Say
class SayTests: XCTestCase {
func testZero() {
XCTAssertEqual("zero", Say.say(0))
}
func testOne() {
XCTAssertEqual("one", Say.say(1))
}
func testFourteen() {
XCTAssertEqual("fourteen", Say.say(14))
}
func testTwenty() {
XCTAssertEqual("twenty", Say.say(20))
}
func testTwentyTwo() {
XCTAssertEqual("twenty-two", Say.say(22))
}
func testOneHundred() {
XCTAssertEqual("one hundred", Say.say(100))
}
func testOneHundredTwentyThree() {
XCTAssertEqual("one hundred twenty-three", Say.say(123))
}
func testOneThousand() {
XCTAssertEqual("one thousand", Say.say(1_000))
}
func testOneThousandTwoHundredThirtyFour() {
XCTAssertEqual("one thousand two hundred thirty-four", Say.say(1_234))
}
func testOneMillion() {
XCTAssertEqual("one million", Say.say(1_000_000))
}
func testOneMillionTwoThousandThreeHundredFortyFive() {
XCTAssertEqual("one million two thousand three hundred forty-five", Say.say(1_002_345))
}
func testOneBillion() {
XCTAssertEqual("one billion", Say.say(1_000_000_000))
}
func testABigNumber() {
XCTAssertEqual("nine hundred eighty-seven billion six hundred fifty-four million three hundred twenty-one thousand one hundred twenty-three", Say.say(987_654_321_123))
}
func testNumbersBelowZeroAreOutOfRange() {
XCTAssertNil(Say.say(-1))
}
func testNumbersAbove999999999999AreOutOfRange() {
XCTAssertNil(Say.say(1_000_000_000_000))
}
static var allTests: [(String, (SayTests) -> () throws -> Void)] {
return [
("testZero", testZero),
("testOne", testOne),
("testFourteen", testFourteen),
("testTwenty", testTwenty),
("testTwentyTwo", testTwentyTwo),
("testOneHundred", testOneHundred),
("testOneHundredTwentyThree", testOneHundredTwentyThree),
("testOneThousand", testOneThousand),
("testOneThousandTwoHundredThirtyFour", testOneThousandTwoHundredThirtyFour),
("testOneMillion", testOneMillion),
("testOneMillionTwoThousandThreeHundredFortyFive", testOneMillionTwoThousandThreeHundredFortyFive),
("testOneBillion", testOneBillion),
("testABigNumber", testABigNumber),
("testNumbersBelowZeroAreOutOfRange", testNumbersBelowZeroAreOutOfRange),
("testNumbersAbove999999999999AreOutOfRange", testNumbersAbove999999999999AreOutOfRange),
]
}
}
```

```
struct Say {
static let firstTwenty: [Int: String] = [
1: "one", 2: "two", 3: "three", 4: "four", 5: "five",
6: "six", 7: "seven", 8: "eight", 9: "nine", 10: "ten",
11: "eleven", 12: "twelve", 13: "thirteen", 14: "fourteen", 15: "fifteen",
16: "sixteen", 17: "seventeen", 18: "eighteen", 19: "nineteen"
]
static let tens: [Int: String] = [
20: "twenty", 30: "thirty", 40: "forty", 50: "fifty",
60: "sixty", 70: "seventy", 80: "eighty", 90: "twenty"
]
static let magnitudes = [1_000_000_000, 1_000_000, 1000, 100]
static let magnitudeNames: [Int: String] = [
1_000_000_000: "billion",
1_000_000: "million",
1000: "thousand",
100: "hundred"
]
static func say(_ number: Int) -> String? {
if number < 0 || number >= 1_000_000_000_000 { return nil }
if number == 0 { return "zero" }
let (counts, remainder) = countsAndRemainder(number: number, magnitudes: magnitudes)
var segments = magnitudes.reduce([String]()) { segments, magnitude in
let count = counts[magnitude]!
return count == 0 ? segments : segments + [numToText(count), magnitudeNames[magnitude]!]
}
if remainder > 0 { segments.append(numToText(remainder)) }
return segments.joined(separator: " ")
}
static func countsAndRemainder(number: Int, magnitudes: [Int]) -> ([Int: Int], Int) {
let initial = ([Int: Int](), number)
return magnitudes.reduce(initial) { acc, magnitude in
var (counts, num) = acc
let (remainder, count) = countForMagnitude(num, magnitude)
counts[magnitude] = count
return (counts, remainder)
}
}
static func countForMagnitude(_ num: Int, _ magnitude: Int) -> (Int, Int) {
var count = 0
var num = num
while num >= magnitude {
count += 1
num -= magnitude
}
return (num, count)
}
static func numToText(_ num: Int) -> String {
assert(num > 0 && num < 1000)
var num = num
var hundreds = 0
while num >= 100 {
hundreds += 1
num -= 100
}
var text = ""
if num < 20 {
text = num > 0 ? firstTwenty[num]! : ""
} else {
var tens = 20
num -= 20
while num > 10 {
tens += 10
num -= 10
}
text = self.tens[tens]!
if num > 0 {
text = "\(text)-\(firstTwenty[num]!)"
}
}
if hundreds > 0 {
text = numToText(hundreds) + " hundred " + text
}
return text
}
}
```

A huge amount can be learned from reading other people’s code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

- What compromises have been made?
- Are there new concepts here that you could read more about to improve your understanding?

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