iOS11 Code Challenge (2020-01-15) - Reverse Only Letters

reverseOnlyLetters.swift

func reverseOnlyLetters(_ inputString: String) -> String {
    let lettersReversed = [Character](
        inputString.compactMap { char -> Character? in
            return char.isLetter ? char : nil
        }.reversed()
    )

    var outputCharacters = [Character](inputString)
    var i = 0
    while i < lettersReversed.count {
        for j in 0..<outputCharacters.count {
            if outputCharacters[j].isLetter {
                outputCharacters[j] = lettersReversed[i]
                i += 1
            }
        }
    }

    let outputString = String(outputCharacters)
    return outputString
}

print(reverseOnlyLetters("ab-cd"))
print(reverseOnlyLetters("a-bC-dEf-ghIj"))
print(reverseOnlyLetters("Test1ng-Leet=code-Q!"))