day1

app/build.gradle.kts

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+/*
+ * This file was generated by the Gradle 'init' task.
+ *
+ * This generated file contains a sample Kotlin application project to get you started.
+ * For more details on building Java & JVM projects, please refer to https://docs.gradle.org/8.10.2/userguide/building_java_projects.html in the Gradle documentation.
+ */
+
+plugins {
+    // Apply the org.jetbrains.kotlin.jvm Plugin to add support for Kotlin.
+    alias(libs.plugins.kotlin.jvm)
+
+    // Apply the application plugin to add support for building a CLI application in Java.
+    application
+}
+
+repositories {
+    // Use Maven Central for resolving dependencies.
+    mavenCentral()
+}
+
+dependencies {
+    // Use the Kotlin JUnit 5 integration.
+    testImplementation("org.jetbrains.kotlin:kotlin-test-junit5")
+
+    // Use the JUnit 5 integration.
+    testImplementation(libs.junit.jupiter.engine)
+
+    testRuntimeOnly("org.junit.platform:junit-platform-launcher")
+
+    // This dependency is used by the application.
+    implementation(libs.guava)
+}
+
+// Apply a specific Java toolchain to ease working on different environments.
+java {
+    toolchain {
+        languageVersion = JavaLanguageVersion.of(21)
+    }
+}
+
+application {
+    // Define the main class for the application.
+    mainClass = "org.example.AppKt"
+}
+
+tasks.named<Test>("test") {
+    // Use JUnit Platform for unit tests.
+    useJUnitPlatform()
+    this.testLogging {
+        this.showStandardStreams = true
+    }
+}

app/src/main/kotlin/org/day01/Day01.kt

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+
+package org.example
+
+import kotlin.io.println
+import kotlin.math.abs
+
+class Day01 {
+    fun parse(input: String): List<List<Int>> {
+        val lhs: MutableList<Int> = mutableListOf()
+        val rhs: MutableList<Int> = mutableListOf()
+
+        for (line in input.lines()) {
+            val split = line.split("   ").map { str -> str.toInt() }
+            lhs.add(split[0])
+            rhs.add(split[1])
+        }
+
+        return listOf(lhs, rhs)
+    }
+
+    fun part1(input: String): Int {
+        val lists = parse(input)
+        val lhs = lists[0].sorted()
+        val rhs = lists[1].sorted()
+
+        var sum = 0
+        for (i in 0..<lhs.count()) {
+            sum += abs(lhs[i] - rhs[i])
+        }
+        return sum;
+    }
+
+    fun part2(input: String): Int {
+        val lists = parse(input)
+        val lhs = lists[0].sorted()
+        val rhs = lists[1].sorted()
+
+        var sum = 0
+        for (i in 0..<lhs.count()) {
+            var rhs_idx = 0
+            val target = lhs[i]
+            var count = 0
+            while (rhs[rhs_idx] < target) {
+                rhs_idx += 1
+            }
+            while (rhs[rhs_idx] == target) {
+                count += 1
+                rhs_idx += 1
+            }
+
+            sum += target * count
+        }
+        return sum
+    }
+}

app/src/main/kotlin/org/example/App.kt

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+/*
+ * This source file was generated by the Gradle 'init' task
+ */
+package org.example
+
+class App {
+    val greeting: String
+        get() {
+            return "Hello World!"
+        }
+}
+
+fun main() {
+    println(App().greeting)
+}

app/src/test/kotlin/org/day01/Day01Test.kt

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+package org.example
+
+import kotlin.test.Test
+import kotlin.test.assertNotNull
+import kotlin.test.assertIs
+
+class Day01Test {
+    @Test fun part1() {
+        val day = Day01()
+        val test = """3   4
+4   3
+2   5
+1   3
+3   9
+3   3"""
+
+        val output = day.part1(test)
+        println(output)
+        assert(output == 11)
+    }
+
+    @Test fun part2() {
+        val day = Day01()
+
+        val test =  """3   4
+4   3
+2   5
+1   3
+3   9
+3   3"""
+
+        val output = day.part2(test)
+        println(output)
+        assert(output == 31)
+    }
+}

app/src/test/kotlin/org/example/AppTest.kt

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+/*
+ * This source file was generated by the Gradle 'init' task
+ */
+package org.example
+
+import kotlin.test.Test
+import kotlin.test.assertNotNull
+
+class AppTest {
+    @Test fun appHasAGreeting() {
+        val classUnderTest = App()
+        assertNotNull(classUnderTest.greeting, "app should have a greeting")
+    }
+}