2023: day 4 part 1

src/main/kotlin/io/plagov/advent/aoc2023/Day04.kt

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+package io.plagov.advent.aoc2023
+
+import kotlin.math.pow
+
+class Day04 {
+
+  fun partOne(input: List<String>): Int {
+    val cards = input.map { cardString -> parseCardString(cardString) }
+    return cards.sumOf { card -> getResultForCard(card) }
+  }
+
+  private fun getResultForCard(card: Card): Int {
+    val count = card.yourNumbers.count { it in card.winningNumbers }
+    return when (count) {
+        1 -> 1
+        2 -> 2
+        else -> 2.toDouble().pow((count - 1)).toInt()
+    }
+  }
+
+  private fun parseCardString(cardString: String): Card {
+    val winningNumbers = cardString
+      .substringAfter(": ").substringBefore(" |")
+      .trim()
+      .split("""\s+""".toRegex())
+      .map { it.toInt() }
+
+    val yourNumbers = cardString
+      .substringAfter("| ")
+      .trim()
+      .split("""\s+""".toRegex())
+      .map { it.toInt() }
+
+    return Card(winningNumbers, yourNumbers)
+  }
+}
+
+data class Card(
+  val winningNumbers: List<Int>,
+  val yourNumbers: List<Int>
+)

src/test/kotlin/io/plagov/advent/aoc2023/Day04Test.kt

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+package io.plagov.advent.aoc2023
+
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.Test
+import util.readInputFile
+
+class Day04Test {
+
+  private val sampleInput = readInputFile("2023/day04-sample.txt")
+
+  private val taskInput = readInputFile("2023/day04.txt")
+
+  private val day04 = Day04()
+
+  @Test
+  fun solveFirstForSampleInput() {
+    assertEquals(13, day04.partOne(sampleInput))
+  }
+
+  @Test
+  fun solveFirstForTaskInput() {
+    assertEquals(123, day04.partOne(taskInput))
+  }
+}

src/test/resources/inputs/2023/day04-sample.txt

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+Card 1: 41 48 83 86 17 | 83 86  6 31 17  9 48 53
+Card 2: 13 32 20 16 61 | 61 30 68 82 17 32 24 19
+Card 3:  1 21 53 59 44 | 69 82 63 72 16 21 14  1
+Card 4: 41 92 73 84 69 | 59 84 76 51 58  5 54 83
+Card 5: 87 83 26 28 32 | 88 30 70 12 93 22 82 36
+Card 6: 31 18 13 56 72 | 74 77 10 23 35 67 36 11