my solution to the task during live coding

test_task_solution_live_coding.kt

data class User(val id: String, val nickname: String)
data class Message(val id: String, val message: String?, val user: User)

val users = listOf(
    User("000", "Bender"),
    User("001", "Leela"),
    User("002", "Fry"),
    User("003", "Zoidberg")
)

val conversation: List<Message> = listOf(
    Message("000", "Hello, I am Fry", users[2]),
    Message("001", "Hello, I am Leela", users[1]),
    Message("002", "Hello, I am Bender", users[2]),
    Message("003", "Hello I am Zoidberg, Whoop, Whoop", users[3]),
    Message("004", "I don't like to fool anyone", users[1]),
    Message("005", "So I will tell you that", users[1]),
    Message("006", "I'm cyclops", users[1]),
    Message("007", "I am captain of a spaceship", users[1]),
    Message("008", "I am the only one of my kind", users[1]),
    Message("009", "and what I want is to meet a man", users[1]),
    Message("010", null, users[3]),
    Message("011", "My Story Is A Lot Like Yours, Only More Interesting ‘Cause It Involves Robots.", users[0]),
    Message("012", "Anything Less Than Immortality Is A Complete Waste Of Time", users[0]),
    Message("013", "Hey sexy mama. Wanna kill all humans?", users[0]),
    Message("014", "Shut Up And Take My Money!", users[2])
)

fun main() {
    println("The most talkative character is: ${getTheMostTalkativeCharacter()}") // Print the name of the most talkative character
    println("Messages by character: ${getMessageGroupedByCharacter()}") // Show all messages grouped by every character
    println("name of the character that said longer sentence : ${longestSentenceSaidBy()}") // Print the name of the character that said longer sentence
    println("Leela messages sorted by size: ${getLeelaMessagesSortedBySize()}") // Show all Leela message sorted by sentence size
}

private fun longestSentenceSaidBy(): String {
    var userWithTheLongestSentence: User? = null
    var longestSentence = ""
    conversation.filter { it.message != null }.forEach {
        if (it.message?.length!! > longestSentence.length) {
            longestSentence = it.message
            userWithTheLongestSentence = it.user
        }
    }
    return userWithTheLongestSentence!!.nickname
}

private fun getTheMostTalkativeCharacter(): String {
    val charactersMap = HashMap<User, Int>()

    conversation.forEach {
        val hits = charactersMap.getOrDefault(it.user, 0)
        charactersMap.put(it.user, hits.inc())
    }

    var theMostTalkativeCharacter: User? = null
    var hits = 0

    charactersMap.forEach {
        if (it.value > hits) {
            theMostTalkativeCharacter = it.key
            hits = it.value
        }
    }
    return theMostTalkativeCharacter!!.nickname
}

private fun getMessageGroupedByCharacter(): HashMap<User, List<String>> {
    val charactersMap = HashMap<User, List<String>>()

    conversation.filter { it.message != null }.forEach {
        val messagesByCharacter = charactersMap.getOrDefault(it.user, ArrayList()).toMutableList()
        messagesByCharacter.add(it.message!!)
        charactersMap.put(it.user, messagesByCharacter)
    }
    return charactersMap;
}

private fun getLeelaMessagesSortedBySize(): List<Message> {
    val leelaMessages = conversation.filter { it.user == users[1] }
    return leelaMessages.filter { it.message != null }.sortedByDescending { it.message!!.length }
}