Harry Potter implemented with Spock

java/harry-potter-spock/.gitignore

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+target/

java/harry-potter-spock/pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+
+  <groupId>org.example</groupId>
+  <artifactId>harry-potter-java</artifactId>
+  <version>1.0-SNAPSHOT</version>
+
+  <properties>
+    <maven.compiler.source>11</maven.compiler.source>
+    <maven.compiler.target>11</maven.compiler.target>
+  </properties>
+
+  <dependencies>
+    <dependency>
+      <groupId>io.vavr</groupId>
+      <artifactId>vavr</artifactId>
+      <version>0.10.3</version>
+    </dependency>
+    <dependency>
+      <groupId>org.projectlombok</groupId>
+      <artifactId>lombok</artifactId>
+      <version>1.18.22</version>
+    </dependency>
+    <dependency>
+      <groupId>org.spockframework</groupId>
+      <artifactId>spock-core</artifactId>
+      <version>2.1-groovy-3.0</version>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>org.codehaus.gmavenplus</groupId>
+        <artifactId>gmavenplus-plugin</artifactId>
+        <version>1.12.1</version>
+        <executions>
+          <execution>
+            <goals>
+              <goal>compileTests</goal>
+            </goals>
+          </execution>
+        </executions>
+      </plugin>
+    </plugins>
+  </build>
+</project>

java/harry-potter-spock/src/main/java/HarryPotter.java

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+import io.vavr.Function1;
+import io.vavr.collection.List;
+import io.vavr.collection.Traversable;
+
+import java.math.BigDecimal;
+
+public class HarryPotter {
+  public static BigDecimal calculatePrice(List<Integer> books) {
+    var distinctBooks = countDistinctBooks(books);
+    var bundlesGreedy = bundleGreedy(distinctBooks);
+    var bundlesAdjusted = adjustBundles(bundlesGreedy);
+    return (BigDecimal) bundlesAdjusted.map(HarryPotter::giveDiscount).sum();
+  }
+
+  public static List<Integer> countDistinctBooks(List<Integer> books) {
+    return books.groupBy(Function1.identity())
+                .mapValues(Traversable::size)
+                .values()
+                .sorted()
+                .toList();
+  }
+
+  public static List<Integer> bundleGreedy(List<Integer> bookSets) {
+    return bookSets
+        .scanLeft(bookSets, (remainingBooks, __) -> removeOneBundle(remainingBooks))
+        .filter(Traversable::nonEmpty)
+        .map(Traversable::size);
+  }
+
+  private static List<Integer> removeOneBundle(List<Integer> remainingBooks) {
+    return remainingBooks.map(it -> it - 1).filter(it -> it > 0);
+  }
+
+  public static List<Integer> adjustBundles(List<Integer> greedyBundles) {
+    var howManyThrees = greedyBundles.count(it -> it == 3);
+    var howManyFives = greedyBundles.count(it -> it == 5);
+    var commonCount = Math.min(howManyThrees, howManyFives);
+    var bundlesOfFour = List.fill(commonCount * 2, 4);
+    var remainingBundlesOfThree = List.fill(howManyThrees - commonCount, 3);
+    var remainingBundlesOfFive = List.fill(howManyFives - commonCount, 5);
+    return greedyBundles.reject(it -> it == 3)
+                        .reject(it -> it == 5)
+                        .appendAll(bundlesOfFour)
+                        .appendAll(remainingBundlesOfThree)
+                        .appendAll(remainingBundlesOfFive);
+  }
+
+  public static BigDecimal giveDiscount(int bundleSize) {
+    return new BigDecimal[]{
+        BigDecimal.valueOf(8),
+        BigDecimal.valueOf(15.2),
+        BigDecimal.valueOf(21.6),
+        BigDecimal.valueOf(25.6),
+        BigDecimal.valueOf(30.0)
+    }[bundleSize - 1];
+  }
+}
+

java/harry-potter-spock/src/test/groovy/HarryPotterTest.groovy

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+import io.vavr.collection.List
+import spock.lang.Specification
+
+class HarryPotterTest extends Specification {
+  def "integration test"() {
+    when: "price is calculated"
+    def price = HarryPotter.calculatePrice(toVavr(books))
+
+    then: "expected price is achieved"
+    price == expected
+
+    where:
+    books                    | expected
+    [1, 2, 3, 4, 5]          | 30.00
+    [1, 1, 2, 2, 3, 3, 4, 5] | 51.20
+  }
+
+  def "count books"() {
+    when: "distinct books are counted"
+    def result = HarryPotter.countDistinctBooks(toVavr(books))
+
+    then: "expected count is returned"
+    result == toVavr(expected)
+
+    where:
+    books                    | expected
+    []                       | []
+    [1]                      | [1]
+    [1, 1]                   | [2]
+    [1, 1, 1]                | [3]
+    [1, 1, 1, 2, 2]          | [2, 3]
+    [1, 1, 2, 2, 3, 3, 4, 5] | [1, 1, 2, 2, 2]
+  }
+
+  def "build greedy bundles"() {
+    when: "count of books are bundled"
+    def greedyBundles = HarryPotter.bundleGreedy(toVavr(count))
+
+    then: "expected bundles are achieved"
+    greedyBundles == toVavr(expected)
+
+    where:
+    count           | expected
+    [1, 1, 2, 2, 2] | [5, 3]
+    [2, 2, 2, 2, 2] | [5, 5]
+    [2, 2, 2, 3, 3] | [5, 5, 2]
+    [2, 2, 2]       | [3, 3]
+    [1, 1, 1]       | [3]
+  }
+
+  def "adjusts bundles swapping 5,3 to 4,4"() {
+    when: "greedy bundles are adjusted to achieve highest discount"
+    def greedyBundles = HarryPotter.adjustBundles(toVavr(bundles))
+
+    then: "expected bundles are achieved"
+    greedyBundles == toVavr(expected)
+
+    where:
+    bundles         | expected
+    []              | []
+    [1, 1, 1]       | [1, 1, 1]
+    [1, 1, 3]       | [1, 1, 3]
+    [5, 3]          | [4, 4]
+    [5, 3, 3]       | [4, 4, 3]
+    [5, 3, 3, 5]    | [4, 4, 4, 4]
+    [5, 3, 3, 5, 3] | [4, 4, 4, 4, 3]
+  }
+
+  def "gives discounts for sets"() {
+    when: "discount is calculated"
+    def result = HarryPotter.giveDiscount(bundleSize)
+
+    then: "expected discount is returned"
+    result == expected
+
+    where:
+    bundleSize | expected
+    1          | 1.0 * 8
+    2          | 0.95 * 2 * 8
+    3          | 0.90 * 3 * 8
+    4          | 0.80 * 4 * 8
+    5          | 0.75 * 5 * 8
+  }
+
+  List<Integer> toVavr(java.util.List<Integer> xs) {
+    List.ofAll(xs)
+  }
+}