Day 7: Bridge Repair

README.md

@@ -11,4 +11,4 @@ Development occurs in language-specific directories:
 |[Day4.hs](hs/src/Day4.hs)|[Day4.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day4.kt)|[day4.py](py/aoc2024/day4.py)|[day4.rs](rs/src/day4.rs)|
 |[Day5.hs](hs/src/Day5.hs)|[Day5.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day5.kt)|[day5.py](py/aoc2024/day5.py)|[day5.rs](rs/src/day5.rs)|
 |[Day6.hs](hs/src/Day6.hs)|[Day6.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day6.kt)|[day6.py](py/aoc2024/day6.py)|[day6.rs](rs/src/day6.rs)|
-|[Day7.hs](hs/src/Day7.hs)||||
+|[Day7.hs](hs/src/Day7.hs)|[Day7.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day7.kt)||[|

kt/aoc2024-exe/src/commonBench/kotlin/com/github/ephemient/aoc2024/exe/Day7Bench.kt

@@ -0,0 +1,31 @@
+package com.github.ephemient.aoc2024.exe
+
+import com.github.ephemient.aoc2024.Day7
+import kotlinx.benchmark.Benchmark
+import kotlinx.benchmark.Blackhole
+import kotlinx.benchmark.Scope
+import kotlinx.benchmark.Setup
+import kotlinx.benchmark.State
+
+@State(Scope.Benchmark)
+class Day7Bench {
+    private lateinit var input: String
+
+    @Setup
+    fun setup() {
+        input = getDayInput(7)
+    }
+
+    @Benchmark
+    fun part1() = Day7(input).part1()
+
+    @Benchmark
+    fun part2() = Day7(input).part2()
+
+    @Benchmark
+    fun both(bh: Blackhole) {
+        val day7 = Day7(input)
+        bh.consume(day7.part1())
+        bh.consume(day7.part2())
+    }
+}

kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day7.kt

@@ -0,0 +1,43 @@
+package com.github.ephemient.aoc2024
+
+class Day7(input: String) {
+    private val equations = input.lineSequence().filter { it.isNotEmpty() }.map { line ->
+        val (lhs, rhs) = line.split(": ", limit = 2)
+        lhs.toLong() to rhs.split(' ').map { it.toLong() }
+    }.toList()
+
+    fun part1() = equations.sumOf { equation ->
+        val stack = mutableListOf(equation)
+        while (stack.isNotEmpty()) {
+            val (x, values) = stack.removeLast()
+            val y = values.last()
+            if (values.size == 1) {
+                if (x == y) return@sumOf equation.first else continue
+            }
+            val rest = values.subList(0, values.lastIndex)
+            if (x >= y) stack.add(x - y to rest)
+            if (x % y == 0L) stack.add(x / y to rest)
+        }
+        0
+    }
+
+    fun part2() = equations.sumOf { equation ->
+        val stack = mutableListOf(equation)
+        while (stack.isNotEmpty()) {
+            val (x, values) = stack.removeLast()
+            val y = values.last()
+            if (values.size == 1) {
+                if (x == y) return@sumOf equation.first else continue
+            }
+            val rest = values.subList(0, values.lastIndex)
+            if (x >= y) stack.add(x - y to rest)
+            if (x % y == 0L) stack.add(x / y to rest)
+            if (x > y) {
+                var d = 10L
+                while (d <= y) d *= 10
+                if (x % d == y) stack.add(x / d to rest)
+            }
+        }
+        0
+    }
+}

kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Days.kt

@@ -7,6 +7,7 @@ val days: List<Day> = listOf(
     Day(4, ::Day4, Day4::part1, Day4::part2),
     Day(5, ::Day5, Day5::part1, Day5::part2),
     Day(6, ::Day6, Day6::part1, Day6::part2),
+    Day(7, ::Day7, Day7::part1, Day7::part2),
 )
 
 data class Day(

kt/aoc2024-lib/src/commonTest/kotlin/com/github/ephemient/aoc2024/Day7Test.kt

@@ -0,0 +1,31 @@
+package com.github.ephemient.aoc2024
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class Day7Test {
+    @Test
+    fun part1() {
+        assertEquals(3749L, Day7(example).part1())
+    }
+
+    @Test
+    fun part2() {
+        assertEquals(11387L, Day7(example).part2())
+    }
+
+    companion object {
+        private val example =
+            """
+            |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
+            |""".trimMargin()
+    }
+}