Merge pull request #616 from exercism/collatz-conjecture

collatz-conjecture: add to track

config.json

@@ -96,6 +96,11 @@
       "topics": []
     },
     {
+      "slug": "collatz-conjecture",
+      "difficulty": 4,
+      "topics": []
+    },
+    {
       "slug": "nth-prime",
       "difficulty": 4,
       "topics": []

exercises/collatz-conjecture/build.gradle

@@ -0,0 +1,18 @@
+apply plugin: "java"
+apply plugin: "eclipse"
+apply plugin: "idea"
+
+repositories {
+    mavenCentral()
+}
+
+dependencies {
+    testCompile "junit:junit:4.12"
+}
+
+test {
+    testLogging {
+        exceptionFormat = 'full'
+        events = ["passed", "failed", "skipped"]
+    }
+}

exercises/collatz-conjecture/src/example/java/CollatzCalculator.java

@@ -0,0 +1,19 @@
+class CollatzCalculator {
+
+    int computeStepCount(final int start) {
+        if (start <= 0) throw new IllegalArgumentException("Only natural numbers are allowed");
+
+        if (start == 1) return 0;
+
+        final int next;
+
+        if (start % 2 == 0) {
+            next = start / 2;
+        } else {
+            next = 3 * start + 1;
+        }
+
+        return 1 + computeStepCount(next);
+    }
+
+}

exercises/collatz-conjecture/src/main/java/CollatzCalculator.java

@@ -0,0 +1,7 @@
+class CollatzCalculator {
+
+    int computeStepCount(int start) {
+        throw new UnsupportedOperationException("Delete this statement and write your own implementation.");
+    }
+
+}

exercises/collatz-conjecture/src/test/java/CollatzCalculatorTest.java

@@ -0,0 +1,59 @@
+import org.junit.Before;
+import org.junit.Ignore;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.ExpectedException;
+
+import static org.junit.Assert.assertEquals;
+
+/*
+ * version: 1.0.0
+ */
+public class CollatzCalculatorTest {
+
+    @Rule
+    public ExpectedException expectedException = ExpectedException.none();
+
+    private CollatzCalculator collatzCalculator;
+
+    @Before
+    public void setUp() {
+        collatzCalculator = new CollatzCalculator();
+    }
+
+    @Test
+    public void testZeroStepsRequiredWhenStartingFrom1() {
+        assertEquals(0, collatzCalculator.computeStepCount(1));
+    }
+
+    @Ignore("Remove to run test")
+    @Test
+    public void testCorrectNumberOfStepsWhenAllStepsAreDivisions() {
+        assertEquals(4, collatzCalculator.computeStepCount(16));
+    }
+
+    @Ignore("Remove to run test")
+    @Test
+    public void testCorrectNumberOfStepsWhenBothStepTypesAreNeeded() {
+        assertEquals(9, collatzCalculator.computeStepCount(12));
+    }
+
+    @Ignore("Remove to run test")
+    @Test
+    public void testZeroIsConsideredInvalidInput() {
+        expectedException.expect(IllegalArgumentException.class);
+        expectedException.expectMessage("Only natural numbers are allowed");
+
+        collatzCalculator.computeStepCount(0);
+    }
+
+    @Ignore("Remove to run test")
+    @Test
+    public void testNegativeIntegerIsConsideredInvalidInput() {
+        expectedException.expect(IllegalArgumentException.class);
+        expectedException.expectMessage("Only natural numbers are allowed");
+
+        collatzCalculator.computeStepCount(-15);
+    }
+
+}

exercises/difference-of-squares/src/main/java/DifferenceOfSquaresCalculator.java

@@ -1,15 +0,0 @@
-final class DifferenceOfSquaresCalculator {
-
-    int computeSquareOfSumTo(final int input) {
-        throw new UnsupportedOperationException("Delete this statement and write your own implementation.");
-    }
-
-    int computeSumOfSquaresTo(final int input) {
-        throw new UnsupportedOperationException("Delete this statement and write your own implementation.");
-    }
-
-    int computeDifferenceOfSquares(final int input) {
-      throw new UnsupportedOperationException("Delete this statement and write your own implementation.");
-    }
-
-}

exercises/settings.gradle

@@ -13,6 +13,7 @@ include 'book-store'
 include 'bracket-push'
 include 'change'
 include 'clock'
+include 'collatz-conjecture'
 include 'crypto-square'
 include 'custom-set'
 include 'diamond'