Complete day 3

2023-12-05 03:58:17 +01:00 · 2023-12-05 03:58:17 +01:00 · 78d272bf7b
parent af4491d09c
commit 78d272bf7b
3 changed files with 267 additions and 0 deletions
--- a/day3/day3.kt
+++ b/day3/day3.kt
@ -0,0 +1,117 @@
+import java.io.File
+
+typealias Coordinate = Pair<Int, Int>
+
+fun main() {
+    val input = File("input")
+
+    var numbers: MutableMap<Coordinate, Int> = mutableMapOf()
+    var symbols: MutableMap<Coordinate, Char> = 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<Int> =
+            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: ${parts.sum()}")
+}
+
+fun nextTo(coordinate: Coordinate): List<Coordinate> {
+    return (coordinate.first - 1..coordinate.first + 1).flatMap { row ->
+        (coordinate.second - 1..coordinate.second + 1).map { col -> Coordinate(row, col) }
+    }
+}
--- a/day3/input
+++ b/day3/input
@ -0,0 +1,140 @@
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--- a/day3/test
+++ b/day3/test
@ -0,0 +1,10 @@
+467..114..
+...*......
+..35..633.
+......#...
+617*......
+.....+.58.
+..592.....
+......755.
+...$.*....
+.664.598..