[2024/4] Ceres Search (Part 2)

pfolta · Dec 4, 2024 · ed6755f · ed6755f
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diff --git a/README.md b/README.md
@@ -26,7 +26,7 @@
 |     2021 |   ★   |   ★   |   ★   |   ★   |   ★   |   ★   |   ★   |   ★   |   ★   |   ★    |   ★    |        |   ★    |   ★    |        |        |        |        |        |        |        |        |        |        |        |    26 |
 |     2022 |   ★   |   ★   |   ★   |   ★   |   ★   |   ★   |   ★   |   ★   |   ★   |   ★    |   ★    |   ★    |   ★    |        |        |        |        |        |        |        |   ☆    |        |        |        |   ☆    |    28 |
 |     2023 |   ★   |   ★   |   ★   |   ★   |   ☆   |   ★   |   ☆   |       |       |        |        |        |        |        |        |        |        |        |        |        |        |        |        |        |        |    12 |
-|     2024 |   ★   |   ★   |   ★   |   ☆   |       |       |       |       |       |        |        |        |        |        |        |        |        |        |        |        |        |        |        |        |        |     7 |
+|     2024 |   ★   |   ★   |   ★   |   ★   |       |       |       |       |       |        |        |        |        |        |        |        |        |        |        |        |        |        |        |        |        |     8 |
 
 ## 🛷 How to run
 
@@ -165,7 +165,7 @@ e.g. `HandyHaversacks`)*
 | [**2024**](https://adventofcode.com/2024) |   1 | [Historian Hysteria](https://adventofcode.com/2024/day/1)                                              | [[Code](src/main/kotlin/adventofcode/year2024/Day01HistorianHysteria.kt)]&nbsp;[[Test](src/test/kotlin/adventofcode/year2024/Day01HistorianHysteriaSpec.kt)]                                 | `1970720`              | `17191599`                                       |
 |                                           |   2 | [Red-Nosed Reports](https://adventofcode.com/2024/day/2)                                               | [[Code](src/main/kotlin/adventofcode/year2024/Day02RedNosedReports.kt)]&nbsp;[[Test](src/test/kotlin/adventofcode/year2024/Day02RedNosedReportsSpec.kt)]                                     | `572`                  | `612`                                            |
 |                                           |   3 | [Mull It Over](https://adventofcode.com/2024/day/3)                                                    | [[Code](src/main/kotlin/adventofcode/year2024/Day03MullItOver.kt)]&nbsp;[[Test](src/test/kotlin/adventofcode/year2024/Day03MullItOverSpec.kt)]                                               | `174960292`            | `56275602`                                       |
-|                                           |   4 | [Ceres Search](https://adventofcode.com/2024/day/4)                                                    | [[Code](src/main/kotlin/adventofcode/year2024/Day04CeresSearch.kt)]&nbsp;[[Test](src/test/kotlin/adventofcode/year2024/Day04CeresSearchSpec.kt)]                                             | `2483`                 |                                                  |
+|                                           |   4 | [Ceres Search](https://adventofcode.com/2024/day/4)                                                    | [[Code](src/main/kotlin/adventofcode/year2024/Day04CeresSearch.kt)]&nbsp;[[Test](src/test/kotlin/adventofcode/year2024/Day04CeresSearchSpec.kt)]                                             | `2483`                 | `1925`                                           |
 
 ## 🕯️ Useful commands
 

diff --git a/src/main/kotlin/adventofcode/year2024/Day04CeresSearch.kt b/src/main/kotlin/adventofcode/year2024/Day04CeresSearch.kt
@@ -6,10 +6,10 @@ import adventofcode.PuzzleInput
 class Day04CeresSearch(customInput: PuzzleInput? = null) : Puzzle(customInput) {
     override fun partOne() = WordSearch(input).countXmas()
 
+    override fun partTwo() = WordSearch(input).countMasCrossed()
+
     companion object {
-        private data class WordSearch(
-            val grid: List<List<Char>>,
-        ) {
+        private data class WordSearch(val grid: List<List<Char>>) {
             private val rows = grid.size
             private val cols = grid.first().size
 
@@ -33,6 +33,21 @@ class Day04CeresSearch(customInput: PuzzleInput? = null) : Puzzle(customInput) {
                     .size
             }
 
+            fun countMasCrossed(): Int {
+                val mas = "MAS"
+                val length = mas.length
+
+                return (0..rows - length).flatMap { row ->
+                    (0..cols - length).map { col ->
+                        val topDiagonal = (0 until length).map { d -> row + d to col + d }
+                        val bottomDiagonal = (0 until length).map { d -> row + length - 1 - d to col + d }
+
+                        setOf(topDiagonal, bottomDiagonal).map { coordinates -> coordinates.map { (x, y) -> grid[x][y] }.joinToString("") }
+                    }
+                }
+                    .count { diagonals -> diagonals.all { diagonal -> diagonal == mas || diagonal == mas.reversed() } }
+            }
+
             companion object {
                 operator fun invoke(input: String) = WordSearch(input.lines().map { row -> row.toList() })
             }

diff --git a/src/test/kotlin/adventofcode/year2024/Day04CeresSearchSpec.kt b/src/test/kotlin/adventofcode/year2024/Day04CeresSearchSpec.kt
@@ -2,4 +2,4 @@ package adventofcode.year2024
 
 import adventofcode.PuzzleBaseSpec
 
-class Day04CeresSearchSpec : PuzzleBaseSpec(18)
+class Day04CeresSearchSpec : PuzzleBaseSpec(18, 9)
Original file line number	Diff line number	Diff line change
Expand Up		@@ -2,4 +2,4 @@ package adventofcode.year2024

		import adventofcode.PuzzleBaseSpec

		class Day04CeresSearchSpec : PuzzleBaseSpec(18)
		class Day04CeresSearchSpec : PuzzleBaseSpec(18, 9)