Day 3

Author: WVerlaek

src/main/kotlin/y24/Day3.kt

@@ -0,0 +1,48 @@
+package y24
+
+import common.puzzle.solvePuzzle
+import common.puzzle.Input
+import common.puzzle.Puzzle
+
+fun main() = solvePuzzle(year = 2024, day = 3) { Day3(it) }
+
+class Day3(val input: Input) : Puzzle {
+    private val mulRegex = Regex("""mul\((\d+),(\d+)\)""")
+
+    override fun solveLevel1(): Any {
+        return mulRegex.findAll(input.string).sumOf {
+            it.groupValues[1].toLong() * it.groupValues[2].toLong()
+        }
+    }
+
+    override fun solveLevel2(): Any {
+        val memory = disableMul(input.string)
+        return mulRegex.findAll(memory).sumOf {
+            it.groupValues[1].toLong() * it.groupValues[2].toLong()
+        }
+    }
+
+    fun disableMul(input: String): String {
+        val result = input.toCharArray()
+
+        var i = 0
+        while (i < input.length) {
+            val nextDont = input.indexOf("don't()", i)
+            if (nextDont == -1) {
+                return result.joinToString("")
+            }
+
+            val nextDo = input.indexOf("do()", nextDont)
+            if (nextDo == -1) {
+                // Clear until end of string.
+                result.fill(' ', nextDont, input.length)
+                return result.joinToString("")
+            }
+
+            result.fill(' ', nextDont, nextDo)
+            i = nextDo
+        }
+
+        return result.joinToString("")
+    }
+}

src/test/kotlin/y24/Day3Test.kt

@@ -0,0 +1,23 @@
+package y24
+
+import common.puzzle.Input
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.Test
+
+internal class Day3Test {
+    private val sample = Input("""
+    xmul(2,4)%&mul[3,7]!@^do_not_mul(5,5)+mul(32,64]then(mul(11,8)mul(8,5))
+    """.trimIndent())
+
+    private val day = Day3(sample)
+
+    @Test
+    fun solveLevel1() {
+        assertEquals(161L, day.solveLevel1())
+    }
+
+    @Test
+    fun solveLevel2() {
+         assertEquals(48L, Day3(Input("xmul(2,4)&mul[3,7]!^don't()_mul(5,5)+mul(32,64](mul(11,8)undo()?mul(8,5))")).solveLevel2())
+    }
+}