diff --git a/day3/day3.kt b/day3/day3.kt new file mode 100644 index 0000000..fbc46d9 --- /dev/null +++ b/day3/day3.kt @@ -0,0 +1,117 @@ +import java.io.File + +typealias Coordinate = Pair + +fun main() { + val input = File("input") + + var numbers: MutableMap = mutableMapOf() + var symbols: MutableMap = mutableMapOf() + + input.useLines { + it.forEachIndexed { row, line -> + line.forEachIndexed { col, char -> + when (char) { + in '0'..'9' -> { + // In this case, we're either starting a new + // number, or in the middle of an existing + // number. + + // We need to mark all previous coordinates as + // well as this one as the full multi-digit + // number, so we need to check the previous + // columns. + var length = 1 + while (numbers.get(Coordinate(row, col - length)) != null) { + length += 1 + } + + // Now we check if the column already has a + // number; if not, we're starting a new one, + // otherwise mark this column as well as any + // previous ones as the new number. + val number = numbers.get(Coordinate(row, col - length + 1)) + if (number == null) { + numbers.put(Coordinate(row, col), char.digitToInt()) + } else { + for (coordinate in col downTo col - length + 1) { + numbers.put( + Coordinate(row, coordinate), + number * 10 + char.digitToInt() + ) + } + } + } + // Dots are ignored + '.' -> Unit + // Collect the coordinates of all symbols, too + else -> symbols.put(Coordinate(row, col), char) + } + } + } + } + + val gears: List = + symbols + .map { symbol -> + if (symbol.value == '*') { + var adjacent = 0 + var last: Int? = null + var ratio = 1 + + for (coord in nextTo(symbol.key)) { + val number = numbers.get(coord) + + if (number != last && number != null) { + last = number + adjacent += 1 + ratio *= number + } + } + + if (adjacent == 2) { + ratio + } else { + null + } + } else { + null + } + } + .filterNotNull() + + println("Part 1: ${gears.sum()}") + + val parts = + symbols.flatMap { symbol -> + nextTo(symbol.key) + .map { + val number = numbers.remove(it) + + if (number == null) { + number + } else { + var prev: Coordinate = it + do { + prev = Coordinate(prev.first, prev.second - 1) + } while (numbers.remove(prev) != null) + + var next: Coordinate = it + do { + next = Coordinate(next.first, next.second + 1) + } while (numbers.remove(next) != null) + + number + } + } + .filterNotNull() + } + + println("Part 2: ${parts.sum()}") +} + +fun nextTo(coordinate: Coordinate): List { + return (coordinate.first - 1..coordinate.first + 1).flatMap { row -> + (coordinate.second - 1..coordinate.second + 1).map { col -> Coordinate(row, col) } + } +} diff --git a/day3/input b/day3/input new file mode 100644 index 0000000..e70b8d2 --- /dev/null +++ b/day3/input @@ -0,0 +1,140 @@ +...........................775.651...............887....79...946...921...493.....942..942.....151....155.................................... 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+...*...... +..35..633. +......#... +617*...... +.....+.58. +..592..... +......755. +...$.*.... +.664.598.. \ No newline at end of file