Day 7 ⭐⭐

README.md

@@ -3,7 +3,7 @@
 |              |               |               |           |               |           |               |           |               |           |
 |-------------:|:-------------:|--------------:|:---------:|--------------:|:---------:|--------------:|:---------:|--------------:|:---------:|
 | **[1][d01]** | **[⭐⭐][s01]** |  **[6][d06]** | [⭐⭐][s06] | **[11][d11]** | [☆☆][s11] | **[16][d16]** | [☆☆][s16] | **[22][d22]** | [☆☆][s22] |
-| **[2][d02]** | **[⭐⭐][s02]** |  **[7][d07]** | [☆☆][s07] | **[12][d12]** | [☆☆][s12] | **[17][d17]** | [☆☆][s17] | **[23][d23]** | [☆☆][s23] |
+| **[2][d02]** | **[⭐⭐][s02]** |  **[7][d07]** | [⭐⭐][s07] | **[12][d12]** | [☆☆][s12] | **[17][d17]** | [☆☆][s17] | **[23][d23]** | [☆☆][s23] |
 | **[3][d03]** | **[⭐⭐][s03]** |  **[8][d08]** | [☆☆][s08] | **[13][d13]** | [☆☆][s13] | **[18][d18]** | [☆☆][s18] | **[24][d24]** | [☆☆][s24] |
 | **[4][d04]** | **[⭐⭐][s04]** |  **[9][d09]** | [☆☆][s09] | **[14][d14]** | [☆☆][s14] | **[19][d19]** | [☆☆][s19] | **[25][d25]** | [☆☆][s25] |
 | **[5][d05]** | **[⭐⭐][s05]** | **[10][d10]** | [☆☆][s10] | **[15][d15]** | [☆☆][s15] | **[20][d20]** | [☆☆][s20] |               |           |

build.gradle.kts

@@ -11,6 +11,7 @@ repositories {
 }
 
 dependencies {
+  implementation("com.github.shiguruikai:combinatoricskt:1.6.0")
   testImplementation(kotlin("test"))
 }
 

src/main/kotlin/Day07.kt

@@ -0,0 +1,30 @@
+import com.github.shiguruikai.combinatoricskt.permutationsWithRepetition
+
+class Day07(input: List<String>) {
+
+    private val equations: List<Equation> = input
+        .map { it.split(": ") }
+        .map { (a, b) -> a.toLong() to b.split(" ").map(String::toLong) }
+
+    private val plus: Operation = Long::plus
+    private val times: Operation = Long::times
+    private val concat: Operation = { a, b -> (a.toString() + b.toString()).toLong() }
+
+    fun part1() = solve(setOf(plus, times))
+    fun part2() = solve(setOf(plus, times, concat))
+
+    private fun solve(operations: Set<Operation>) = equations
+        .filter { it(operations) }
+        .sumOf { it.value }
+
+    private operator fun Equation.invoke(operations: Set<Operation>): Boolean = operations
+        .permutationsWithRepetition(numbers.size - 1)
+        .any { value == numbers.reduceIndexed { index, acc, i -> it[index - 1](acc, i) } }
+
+}
+
+typealias Equation = Pair<Long, List<Long>>
+typealias Operation = (Long, Long) -> Long
+
+val Equation.value get() = first
+val Equation.numbers get() = second

src/test/kotlin/Day07Test.kt

@@ -0,0 +1,49 @@
+import Resources.readLines
+import org.junit.jupiter.api.DisplayName
+import org.junit.jupiter.api.Nested
+import org.junit.jupiter.api.Test
+import kotlin.test.assertEquals
+
+@DisplayName("Day 07")
+class Day07Test {
+
+    private val sampleInput = readLines("Day07-sample.txt")
+    private val actualInput = readLines("Day07.txt")
+
+    @Nested
+    @DisplayName("Part 1")
+    inner class Part1 {
+
+        @Test
+        fun `Matches example`() = assertEquals(
+            expected = 3749,
+            actual = Day07(sampleInput).part1(),
+        )
+
+        @Test
+        fun `Actual answer`() = assertEquals(
+            expected = 12940396350192,
+            actual = Day07(actualInput).part1(),
+        )
+
+    }
+
+    @Nested
+    @DisplayName("Part 2")
+    inner class Part2 {
+
+        @Test
+        fun `Matches example`() = assertEquals(
+            expected = 11387,
+            actual = Day07(sampleInput).part2(),
+        )
+
+        @Test
+        fun `Actual answer`() = assertEquals(
+            expected = 106016735664498,
+            actual = Day07(actualInput).part2(),
+        )
+
+    }
+
+}

src/test/resources/Day07-sample.txt

@@ -0,0 +1,9 @@
+190: 10 19
+3267: 81 40 27
+83: 17 5
+156: 15 6
+7290: 6 8 6 15
+161011: 16 10 13
+192: 17 8 14
+21037: 9 7 18 13
+292: 11 6 16 20