Day 06 2025 (#300)

Author: peckb1

src/main/kotlin/me/peckb/aoc/_2025/calendar/day06/Day06.kt

@@ -0,0 +1,104 @@
+package me.peckb.aoc._2025.calendar.day06
+
+import javax.inject.Inject
+import me.peckb.aoc.generators.InputGenerator.InputGeneratorFactory
+import kotlin.text.trim
+
+class Day06 @Inject constructor(
+  private val generatorFactory: InputGeneratorFactory,
+) {
+  companion object {
+    const val PRODUCT = '*'
+    const val SUM = '+'
+  }
+
+  fun partOne(filename: String) = generatorFactory.forFile(filename).read { input ->
+    val numbersInEquations = mutableListOf<MutableList<Long>>()
+    val operationsInEquations = mutableListOf<Char>()
+
+    val newList = { i : Int -> mutableListOf<Long>().also {
+      numbersInEquations.add(i, it)
+    }}
+
+    input.forEach { line ->
+      line.trim().split("\\s+".toRegex()).forEachIndexed { index, dataElement ->
+        val number = dataElement.toLongOrNull()
+          if (number != null) {
+            numbersInEquations.getOrElse(index) { i -> newList(i) }.add(number)
+          } else {
+            operationsInEquations.add(index, dataElement.first())
+          }
+      }
+    }
+
+    numbersInEquations.zip(operationsInEquations).sumOf { (numbers, operation) ->
+      when (operation) {
+        SUM     -> numbers.reduce(Long::plus)
+        PRODUCT -> numbers.reduce(Long::times)
+        else    -> throw IllegalArgumentException("Illegal operation $operation")
+      }
+    }
+  }
+
+  fun partTwo(filename: String) = generatorFactory.forFile(filename).read { input ->
+    val numberLines = mutableListOf<String>()
+    val operationData = mutableListOf<Pair<Char, Int>>()
+
+    var combinedTotal = 0L
+
+    // first we need to find out column spacing and operand data
+    input.forEach { line ->
+      val firstChar = line.first()
+      if (firstChar == PRODUCT || firstChar == SUM) {
+        var index = 0
+        while(index < line.length) {
+          val operation = line[index]
+          if (index == line.length - 1) {
+            // end row so our "length" should use the longest length line
+            val length = (numberLines.maxOf { it.length } - line.length + 1)
+            // and once we have our length, track the operation
+            // since we're at the end of our input string we don't have a buffer space
+            operationData.add(operation to length)
+            index++
+          } else {
+            // not the end row - go char by char until we find the next operand
+            var length = 0
+            do { val next = line[index + ++length] } while (next == ' ')
+            // and once we have our length, track the operation
+            // there is always a buffer space between equations so offset by that
+            operationData.add(operation to length - 1)
+            index += length
+          }
+        }
+      } else {
+        numberLines.add(line)
+      }
+
+      // now that we have our operand and column length we can do math!
+      var bufferIndex = 0
+      operationData.forEach { (operation, dataSize) ->
+        var total = if (operation == PRODUCT) 1L else 0L
+        var digitIndex = 0
+
+        while (digitIndex < dataSize) {
+          val digit = numberLines.map { line ->
+            // grab the number to use, the blank space in the string, ...
+            // or the string wasn't that long and pretend we have trailing spaces
+            line.getOrElse(bufferIndex + dataSize - digitIndex - 1) { ' ' }
+          }.joinToString(separator = "").trim().toLong()
+
+          if (operation == PRODUCT) total *= digit else total += digit
+
+          digitIndex++
+        }
+
+        // don't forget the buffer space when incrementing
+        bufferIndex += dataSize + 1
+        // and track the total math sum
+        combinedTotal += total
+      }
+    }
+
+    combinedTotal
+  }
+}

src/main/kotlin/me/peckb/aoc/_2025/calendar/day06/README.md

@@ -0,0 +1 @@
+## [Day 6: Trash Compactor](https://adventofcode.com/2025/day/6)

src/test/kotlin/me/peckb/aoc/_2025/TestDayComponent.kt

@@ -5,6 +5,7 @@ import me.peckb.aoc._2025.calendar.day02.Day02Test
 import me.peckb.aoc._2025.calendar.day03.Day03Test
 import me.peckb.aoc._2025.calendar.day04.Day04Test
 import me.peckb.aoc._2025.calendar.day05.Day05Test
+import me.peckb.aoc._2025.calendar.day06.Day06Test
 import javax.inject.Singleton
 import me.peckb.aoc.DayComponent
 import me.peckb.aoc.InputModule
@@ -18,4 +19,5 @@ internal interface TestDayComponent : DayComponent {
   fun inject(day03Test: Day03Test)
   fun inject(day04Test: Day04Test)
   fun inject(day05Test: Day05Test)
+  fun inject(day06Test: Day06Test)
 }

src/test/kotlin/me/peckb/aoc/_2025/calendar/day06/Day06Test.kt

@@ -0,0 +1,32 @@
+package me.peckb.aoc._2025.calendar.day06
+
+import javax.inject.Inject
+
+import me.peckb.aoc._2025.DaggerTestDayComponent
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.BeforeEach
+import org.junit.jupiter.api.Test
+
+internal class Day06Test {
+  @Inject
+  lateinit var day06: Day06
+
+  @BeforeEach
+  fun setup() {
+    DaggerTestDayComponent.create().inject(this)
+  }
+
+  @Test
+  fun testDay06PartOne() {
+    assertEquals(4583860641327, day06.partOne(DAY_06))
+  }
+
+  @Test
+  fun testDay06PartTwo() {
+    assertEquals(11602774058280, day06.partTwo(DAY_06))
+  }
+
+  companion object {
+    private const val DAY_06: String = "advent-of-code-input/2025/day06.input"
+  }
+}