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object Day10 {
private enum class ChunkDelimiter(val open: Char, val close: Char) {
Parentheses('(', ')'),
Brackets('[', ']'),
Braces('{', '}'),
Angled('<', '>');
companion object {
fun isOpening(character: Char): Boolean = values().any { it.open == character }
fun isClosing(character: Char): Boolean = values().any { it.close == character }
fun from(character: Char): ChunkDelimiter =
values().find { it.open == character || it.close == character }!!
}
}
private sealed class SyntaxError {
object None : SyntaxError()
class IncompleteLine(private val stack: ArrayDeque<ChunkDelimiter>) : SyntaxError() {
val score: Long
get() {
fun delimiterValue(delimiter: ChunkDelimiter): Int = when (delimiter) {
ChunkDelimiter.Parentheses -> 1
ChunkDelimiter.Brackets -> 2
ChunkDelimiter.Braces -> 3
ChunkDelimiter.Angled -> 4
}
return stack.fold(0) { acc, elem -> acc * 5 + delimiterValue(elem) }
}
}
class CorruptedLine(private val invalidDelimiter: ChunkDelimiter) : SyntaxError() {
val score: Int
get() = when (invalidDelimiter) {
ChunkDelimiter.Parentheses -> 3
ChunkDelimiter.Brackets -> 57
ChunkDelimiter.Braces -> 1197
ChunkDelimiter.Angled -> 25137
}
}
}
private fun parse(line: String): SyntaxError {
val stack = ArrayDeque<ChunkDelimiter>()
for (char in line) {
when {
ChunkDelimiter.isOpening(char) -> stack.addFirst(ChunkDelimiter.from(char))
ChunkDelimiter.isClosing(char) -> {
val closingDelimiter = ChunkDelimiter.from(char)
if (stack.first() == closingDelimiter) {
stack.removeFirst()
} else {
return SyntaxError.CorruptedLine(closingDelimiter)
}
}
}
}
if (stack.isNotEmpty()) {
return SyntaxError.IncompleteLine(stack)
}
return SyntaxError.None
}
fun part1(input: List<String>): Int = input
.map { parse(it) }
.filterIsInstance<SyntaxError.CorruptedLine>()
.sumOf { it.score }
fun part2(input: List<String>): Long =
input
.asSequence()
.map { parse(it) }
.filterIsInstance<SyntaxError.IncompleteLine>()
.map { it.score }
.sorted()
.toList()
.let { it[it.size / 2] }
}
fun main() {
val testInput = readInputAsLines("Day10_test")
check(Day10.part1(testInput) == 26397)
check(Day10.part2(testInput) == 288957L)
val input = readInputAsLines("Day10")
println(Day10.part1(input))
println(Day10.part2(input))
}
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