[2024/2] Red-Nosed Reports (Part 2)

pfolta · Dec 2, 2024 · 0862e77 · 0862e77
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diff --git a/README.md b/README.md
@@ -24,7 +24,7 @@
 <a href="https://adventofcode.com/2021"><img src="https://img.shields.io/badge/%E2%AD%90%202021-26%2F50-0f0f23" alt="2021 Progress" /></a>  
 <a href="https://adventofcode.com/2022"><img src="https://img.shields.io/badge/%E2%AD%90%202022-28%2F50-0f0f23" alt="2022 Progress" /></a>  
 <a href="https://adventofcode.com/2023"><img src="https://img.shields.io/badge/%E2%AD%90%202023-12%2F50-0f0f23" alt="2023 Progress" /></a>  
-<a href="https://adventofcode.com/2024"><img src="https://img.shields.io/badge/%E2%AD%90%202024-3%2F50-0f0f23" alt="2024 Progress" /></a>
+<a href="https://adventofcode.com/2024"><img src="https://img.shields.io/badge/%E2%AD%90%202024-4%2F50-0f0f23" alt="2024 Progress" /></a>
 
 ## 🛷 How to run
 
@@ -161,7 +161,7 @@ e.g. `HandyHaversacks`)*
 |                                           |   6 | [Wait For It](https://adventofcode.com/2023/day/6)                                                     | [[Code](src/main/kotlin/adventofcode/year2023/Day06WaitForIt.kt)]&nbsp;[[Test](src/test/kotlin/adventofcode/year2023/Day06WaitForItSpec.kt)]                                                 | `2269432`              | `35865985`                                       |
 |                                           |   7 | [Camel Cards](https://adventofcode.com/2023/day/7)                                                     | [[Code](src/main/kotlin/adventofcode/year2023/Day07CamelCards.kt)]&nbsp;[[Test](src/test/kotlin/adventofcode/year2023/Day07CamelCardsSpec.kt)]                                               | `250474325`            |                                                  |
 | [**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`                  |                                                  |
+|                                           |   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`                                            |
 
 ## 🕯️ Useful commands
 

diff --git a/src/main/kotlin/adventofcode/year2024/Day02RedNosedReports.kt b/src/main/kotlin/adventofcode/year2024/Day02RedNosedReports.kt
@@ -7,28 +7,31 @@ import kotlin.math.abs
 class Day02RedNosedReports(customInput: PuzzleInput? = null) : Puzzle(customInput) {
     override val name = "Red-Nosed Reports"
 
-    override fun partOne() =
-        input
-            .lines()
-            .map { report -> report.split(" ").mapNotNull(String::toIntOrNull) }
-            .count { report -> report.isSafeReport() }
+    private val reports by lazy {
+        input.lines().map { report -> report.split(" ").mapNotNull(String::toIntOrNull) }
+    }
+
+    override fun partOne() = reports.count { report -> report.isSafeReport() }
+
+    override fun partTwo() = reports.count { report -> report.isAlmostSafeReport() }
 
     companion object {
-        private fun List<Int>.isSafeReport(): Boolean {
-            val change =
-                this
-                    .zipWithNext()
-                    .map { (a, b) -> b - a }
-
-            if (!change.all { it > 0 } && !change.all { it < 0 }) {
-                return false
-            }
+        private fun List<Int>.isSafeReport() = (isStrictlyIncreasing() || isStrictlyDecreasing()) && differsByAtLeast1AndAtMost3()
 
-            if (change.any { abs(it) > 3 }) {
-                return false
+        private fun List<Int>.isAlmostSafeReport(): Boolean {
+            for (i in -1 until size) {
+                if (filterIndexed { j, _ -> i != j }.isSafeReport()) {
+                    return true
+                }
             }
 
-            return true
+            return false
         }
+
+        private fun List<Int>.isStrictlyIncreasing() = zipWithNext().all { (a, b) -> a < b }
+
+        private fun List<Int>.isStrictlyDecreasing() = zipWithNext().all { (a, b) -> a > b }
+
+        private fun List<Int>.differsByAtLeast1AndAtMost3() = zipWithNext().all { (a, b) -> abs(a - b) in 1..3 }
     }
 }
diff --git a/src/test/kotlin/adventofcode/year2024/Day02RedNosedReportsSpec.kt b/src/test/kotlin/adventofcode/year2024/Day02RedNosedReportsSpec.kt
@@ -2,4 +2,4 @@ package adventofcode.year2024
 
 import adventofcode.PuzzleBaseSpec
 
-class Day02RedNosedReportsSpec : PuzzleBaseSpec(2)
+class Day02RedNosedReportsSpec : PuzzleBaseSpec(2, 4)
Original file line number	Diff line number	Diff line change
Expand Up		@@ -2,4 +2,4 @@ package adventofcode.year2024

		import adventofcode.PuzzleBaseSpec

		class Day02RedNosedReportsSpec : PuzzleBaseSpec(2)
		class Day02RedNosedReportsSpec : PuzzleBaseSpec(2, 4)