2025, Day 6

Author: edgars-supe

.idea/runConfigurations/2025__Day_6.xml

@@ -119,4 +119,17 @@ fun <T> List<T>.allEqual(): Boolean {
     if (isEmpty()) return false
     val first = first()
     return drop(1).all { it == first }
-}
+}
+
+fun <T> List<List<T>>.transposed(): List<List<T>> {
+    require(isNotEmpty()) { "Matrix must not be empty." }
+    val rowCount = size
+    val colCount = first().size
+    require(all { it.size == colCount }) { "All rows must have the same length." }
+
+    return List(colCount) { col ->
+        List(rowCount) { row ->
+            elementAt(row).elementAt(col)
+        }
+    }
+}

src/main/kotlin/lv/esupe/aoc/utils/ListUtil.kt

@@ -13,4 +13,29 @@ inline fun String.charByChar(other: String, crossinline block: (Char?, Char?) ->
 
 fun String.count(char: Char): Int = count { it == char }
 
-fun String.findAllInts(): List<Int> = NUMBER_REGEX.findAll(this).map { it.value.toInt() }.toList()
+fun String.findAllInts(): List<Int> = NUMBER_REGEX.findAll(this).map { it.value.toInt() }.toList()
+
+fun List<String>.transposed(): List<String> {
+    require(isNotEmpty()) { "Input must not be empty." }
+    val width = first().length
+    require(all { it.length == width }) { "All strings must have the same length." }
+
+    return List(width) { col ->
+        buildString(size) {
+            for (row in this@transposed.indices) {
+                this.append(this@transposed[row][col])
+            }
+        }
+    }
+}
+
+fun List<String>.rotated90(ccw: Boolean): List<String> {
+    return if (ccw) {
+        transposed().reversed()
+    } else {
+        transposed().map { it.reversed() }
+    }
+}
+
+fun List<String>.rotated180(): List<String> =
+    reversed().map { it.reversed() }

src/main/kotlin/lv/esupe/aoc/utils/String.kt

@@ -0,0 +1,44 @@
+package lv.esupe.aoc.year2025
+
+import lv.esupe.aoc.Puzzle
+import lv.esupe.aoc.solve
+import lv.esupe.aoc.utils.chunkedBy
+import lv.esupe.aoc.utils.transposed
+
+fun main() = solve { Day6() }
+
+class Day6 : Puzzle<Long, Long>(2025, 6) {
+    override val input = rawInput
+
+    override fun solvePartOne(): Long {
+        val lines = input.map { line -> line.trim().split(Regex("\\s+")) }
+        val operands = (0 until lines.lastIndex)
+            .map { row -> lines[row].map { it.toLong() } }
+        val ops = lines.last()
+
+        return ops.indices
+            .sumOf { idx ->
+                val op: Long.(Long) -> Long = if (ops[idx] == "*") Long::times else Long::plus
+                operands
+                    .map { it[idx] }
+                    .reduce(op)
+            }
+    }
+
+    override fun solvePartTwo(): Long {
+        return input.transposed()
+            .chunkedBy { it.isBlank() }
+            .sumOf { lines ->
+                val op: Long.(Long) -> Long = if (lines.first().last() == '*') Long::times else Long::plus
+                lines
+                    .map { line -> line.extractNumber() }
+                    .reduce(op)
+            }
+    }
+
+    private fun String.extractNumber(): Long {
+        return fold(0) { acc, i ->
+            if (i.isDigit()) acc * 10 + i.digitToInt() else acc
+        }
+    }
+}

src/main/kotlin/lv/esupe/aoc/year2025/Day6.kt

@@ -31,4 +31,23 @@ class ListTest {
             assertNull(list.atOrNull(-4))
         }
     }
+
+    @Nested
+    inner class Transpose {
+        @Test
+        fun `transpose correctly transposes a matrix`() {
+            val input = listOf(
+                listOf('0', '1', '2'),
+                listOf('3', '4', '5'),
+                listOf('6', '7', '8'),
+                listOf('9', 'a', 'b')
+            )
+            val expected = listOf(
+                listOf('0', '3', '6', '9'),
+                listOf('1', '4', '7', 'a'),
+                listOf('2', '5', '8', 'b')
+            )
+            assertEquals(expected, input.transposed())
+        }
+    }
 }

src/test/kotlin/lv/esupe/aoc/utils/ListTest.kt

@@ -0,0 +1,81 @@
+package lv.esupe.aoc.utils
+
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.Nested
+import org.junit.jupiter.api.Test
+
+class StringTest {
+    @Nested
+    inner class Transposed {
+        @Test
+        fun `transposed correctly transforms list of Strings`() {
+            val input = listOf(
+                "012",
+                "345",
+                "678",
+                "9ab"
+            )
+            val expected = listOf(
+                "0369",
+                "147a",
+                "258b"
+            )
+            assertEquals(expected, input.transposed())
+        }
+    }
+
+    @Nested
+    inner class Rotated90 {
+        @Test
+        fun `Rotated90 correctly rotates list of Strings clockwise`() {
+            val input = listOf(
+                "012",
+                "345",
+                "678",
+                "9ab"
+            )
+            val expected = listOf(
+                "9630",
+                "a741",
+                "b852"
+            )
+            assertEquals(expected, input.rotated90(ccw = false))
+        }
+
+        @Test
+        fun `Rotated90 correctly rotates list of Strings counter-clockwise`() {
+            val input = listOf(
+                "012",
+                "345",
+                "678",
+                "9ab"
+            )
+            val expected = listOf(
+                "258b",
+                "147a",
+                "0369"
+            )
+            assertEquals(expected, input.rotated90(ccw = true))
+        }
+    }
+
+    @Nested
+    inner class Rotated180 {
+        @Test
+        fun `Rotated180 correctly rotates list of Strings`() {
+            val input = listOf(
+                "012",
+                "345",
+                "678",
+                "9ab"
+            )
+            val expected = listOf(
+                "ba9",
+                "876",
+                "543",
+                "210"
+            )
+            assertEquals(expected, input.rotated180())
+        }
+    }
+}

src/test/kotlin/lv/esupe/aoc/utils/StringTest.kt

@@ -0,0 +1,13 @@
+package lv.esupe.aoc.year2025
+
+import lv.esupe.aoc.DayTest
+import org.junit.jupiter.api.Test
+
+class Day6Test : DayTest<Long, Long>() {
+    override val puzzle = { Day6() }
+
+    @Test
+    fun day6_1() {
+        runTest("_1", 4277556, 3263827)
+    }
+}

src/test/kotlin/lv/esupe/aoc/year2025/Day6Test.kt

@@ -0,0 +1,4 @@
+123 328  51 64 
+ 45 64  387 23 
+  6 98  215 314
+*   +   *   +