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enum class ChunkDelimeter(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): ChunkDelimeter = values().find { it.open == character || it.close == character }!!
}
}
sealed class SyntaxError {
object None : SyntaxError()
class IncompleteLine(private val stack: ArrayDeque<ChunkDelimeter>) : SyntaxError() {
val score: Long
get() {
fun delimeterValue(delimeter: ChunkDelimeter): Int = when (delimeter) {
ChunkDelimeter.Parentheses -> 1
ChunkDelimeter.Brackets -> 2
ChunkDelimeter.Braces -> 3
ChunkDelimeter.Angled -> 4
}
return stack.fold(0) { acc, elem -> acc * 5 + delimeterValue(elem) }
}
}
class CorruptedLine(private val invalidDelimeter: ChunkDelimeter) : SyntaxError() {
val score: Int
get() = when (invalidDelimeter) {
ChunkDelimeter.Parentheses -> 3
ChunkDelimeter.Brackets -> 57
ChunkDelimeter.Braces -> 1197
ChunkDelimeter.Angled -> 25137
}
}
}
fun parse(line: String): SyntaxError {
val stack = ArrayDeque<ChunkDelimeter>()
for (char in line) {
when {
ChunkDelimeter.isOpening(char) -> stack.addFirst(ChunkDelimeter.from(char))
ChunkDelimeter.isClosing(char) -> {
val closingDelimeter = ChunkDelimeter.from(char)
if (stack.first() == closingDelimeter) {
stack.removeFirst()
} else {
return SyntaxError.CorruptedLine(closingDelimeter)
}
}
}
}
if (stack.isNotEmpty()) {
return SyntaxError.IncompleteLine(stack)
}
return SyntaxError.None
}
fun main() {
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] }
val testInput = readInputAsLines("Day10_test")
check(part1(testInput) == 26397)
check(part2(testInput) == 288957L)
val input = readInputAsLines("Day10")
println(part1(input))
println(part2(input))
}
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