Hackerrank - Repeated String

Hackerrank_RepeatedString.playground

import Foundation

func getLetterCount(s: String) -> Int {
    return s.filter { $0 == "a" }.count
}

func repeatedString(s: String, n: Int) -> Int {
    let stringCount = s.count
    let remainder = n % stringCount
    let multiplier = n / stringCount
    let prefix = String(s.prefix(remainder))
    let patternPrefix = getLetterCount(s: prefix)
    let aValue = getLetterCount(s: s) * multiplier
    return aValue + patternPrefix
}

repeatedString(s: "abcac", n: 10)           // expected 4
repeatedString(s: "aba", n: 10)             // expected 7
repeatedString(s: "gfcaaaecbg", n: 547602)  // expected 164280
repeatedString(s: "aab", n: 882787)         // expected 588525
repeatedString(s: "ceebbcb", n: 817723)     // expected 0