fun <T> List<T>.rlePreprocess(): List<List<T>> {
    val result = mutableListOf<MutableList<T>>(mutableListOf<T>(this[0]))
    for (i in 0 until lastIndex)
        if (this[i+1] == this[i])
            result.last().add(this[i+1])
        else
            result.add(mutableListOf(this[i+1]))
    return result
}