Coding problem posted on twitter. The twitter thread has interesting solutions in different languages. This one is in swift

splitter.swift

// Original Tweet: https://twitter.com/Al_Grigor/status/1357028887209902088

// input : "aaaabbbcca"
// output: [("a", 4), ("b", 3), ("c", 2), ("a", 1)]


func splitter(str: String) -> [(String, Int)] {
    
    // 01 This will give you an Array of letters
    let letters = str.map { String($0) }
    
    // 02 Stuff we want to track
    var characterCount: Int = 0
    var current: String = ""
    let maxCount = letters.count - 1

    // 03 Our final output. An array of Tuples
    var record: [(String, Int)] = []


    // 04 We loop through each letter, with the index position
    for (index, letter) in letters.enumerated() {
        if letter == current {
            characterCount += 1
            if index == maxCount {
                record.append((current, characterCount))
            }
        } else if current == "" {
            current = letter
            characterCount += 1
        } else {
            record.append((current, characterCount))
            characterCount = 1
            current = letter
            if index == maxCount {
                record.append((current, characterCount))
            }
        }
    }

    // 05 Done
    return record
    
}


splitter(str: "aaaabbbcca")

// This returns
// [("a", 4), ("b", 3), ("c", 2), ("a", 1)]