fun main(args: Array<String>) {
    //part 1
    println(lengthLeft(input))

    //part 2
    input.toLowerCase().asSequence().distinct().map { c ->
        lengthLeft(input.filter { !it.equals(c, ignoreCase = true) })
    }.min().also { println(it) }
}

fun lengthLeft(polymer: String): Int {
    val list = LinkedList(polymer.toList())

    val iter = list.listIterator()
    while (true) {
        val a = if (iter.hasNext()) iter.next() else break
        val b = if (iter.hasNext()) iter.next() else break

        if (a != b && a.equals(b, ignoreCase = true)) {
            iter.remove()
            iter.previous()
            iter.remove()
            if (iter.hasPrevious())
                iter.previous()
        } else {
            iter.previous()
        }
    }

    return list.size
}