fun process(input:String, part2: Boolean = false):Sequence<Int> = buildSequence {

    var skip = false
    var garbage = false
    var level = 0
    var discarded = 0

    input.forEach {
        when {
            skip -> skip = false
            it == '!' && garbage -> skip = true
            it == '>' && garbage -> garbage = false
            it == '<' && !garbage -> garbage = true
            it == '{' && !garbage -> { level++ ; yield (level)}
            it == '}' && !garbage -> if (level > 0) level--
            garbage -> discarded ++
        }
    }
    if (part2) yield (discarded)  // Last element in the list is the number of discarded characters
}