CountCharactersInARow.swift

var countCharactersInRow = getCharactersInARowCount(fromString: "aaaabbbcca")


func getCharactersInARowCount(fromString string: String) -> [[Character: Int]] {
    print("Given string: ", string)
    guard !string.isEmpty else { return []}

    let charactersArray: [Character] = string.map { $0 }
    var collectedData: [[Character: Int]] = []
    var lastCharacter: Character = charactersArray.first!
    var arrayPossition: Int = 0

    charactersArray.forEach { (character) in
        lastCharacter = character

        if collectedData.isEmpty {
            collectedData.append([character:1])
        } else {
            if lastCharacter == character, let characterValue = collectedData[arrayPossition][character] {
                collectedData[arrayPossition][character] = characterValue + 1
            }  else {
                collectedData.append([character: 1])
                arrayPossition += 1
            }
        }
    }
    print("Result for given string: ", collectedData)
    return collectedData
}

// Console prints:
// Given string:  aaaabbbcca
// Result for given string:  [["a": 4], ["b": 3], ["c": 2], ["a": 1]]