import Foundation

func getLetterFrequency(cipherText: String) -> [(String, Int)] {
    let alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
    var frequencies = alphabet.characters.flatMap { (String($0), 0) }

    cipherText.characters.forEach { letter in
        guard let alphabetRange = alphabet.range(of: String(letter).uppercased()) else { return }
        let letterIndex = alphabet.distance(from: alphabet.startIndex, to: alphabetRange.lowerBound)
        let newValue = frequencies[letterIndex].1 + 1
        frequencies[letterIndex] = (frequencies[letterIndex].0, newValue)
    }

    return frequencies
}

let cipherText = "asdfjkashdfiuewfzxvbeirlureasdhabaweqwertyyupoiualskdffhzxmcvb"
let frequencies = getLetterFrequency(cipherText: cipherText)
frequencies.forEach { print($0) }