Discussion on: Daily Challenge #115 - Look and Say Sequence

[Jon Bristow]

Kotlin, because I'm prepping a mini talk on declarative style...

tailrec fun speak(
    remaining: String,
    curr: String = "",
    currCount: Int = 0,
    output: String = ""
): String {
    return when {
        remaining.isEmpty() && curr.isBlank() -> output
        remaining.isEmpty() -> "$output$currCount$curr"
        curr.isEmpty() -> speak(
            remaining.substring(1),
            curr = remaining.substring(0, 1),
            currCount = 1,
            output = output
        )
        remaining.startsWith(curr) -> speak(
            remaining.substring(1),
            curr = curr,
            currCount = currCount + 1,
            output = output
        )
        else -> speak(
            remaining.substring(1),
            curr = remaining.substring(0, 1),
            currCount = 1,
            output = "$output$currCount$curr"
        )
    }
}

fun lookAndSaySequence(input: String, times: Int): String {
    require(times > 0) { "times must be > 0" }
    return generateSequence(input) { speak(it) }.drop(times-1).first()
}

SPOILERS: base64decode('SXQncyBqdXN0IHJ1bi1sZW5ndGgtZW5jb2Rpbmch')

bonus:

lookAndSaySequence("aardvark", 5) === "3112311a13211r13211d13211v13211a13211r13211k"
lookAndSaySequence("Billions and Billions", 3) === "111B111i121l111i111o111n111s111 111a111n111d111 111B111i121l111i111o111n111s"