difference-of-squares: add to track

config.json

@@ -42,7 +42,8 @@
     "linked-list",
     "nth-prime",
     "pascals-triangle",
-    "beer-song"
+    "beer-song",
+    "difference-of-squares"
   ],
   "exercises": [
     {
@@ -239,6 +240,11 @@
       "slug": "beer-song",
       "difficulty": 1,
       "topics": []
+    },
+    {
+      "slug": "difference-of-squares",
+      "difficulty": 1,
+      "topics": []
     }
   ],
   "deprecated": [

exercises/difference-of-squares/build.gradle

@@ -0,0 +1,17 @@
+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/difference-of-squares/src/example/java/Difference.java

@@ -0,0 +1,20 @@
+import java.util.stream.IntStream;
+
+public final class Difference {
+
+    public static int computeSquareOfSumTo(final int input) {
+        final int sum = input * (input + 1) / 2;
+        return (int) Math.pow(sum, 2);
+    }
+
+    public static int computeSumOfSquaresTo(final int input) {
+        return IntStream.rangeClosed(1, input)
+                .map(i -> (int) Math.pow(i, 2))
+                .sum();
+    }
+
+    public static int betweenSquareOfSumAndSumOfSquaresTo(final int input) {
+        return computeSquareOfSumTo(input) - computeSumOfSquaresTo(input);
+    }
+
+}

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

@@ -0,0 +1,5 @@
+public final class Difference {
+    
+
+
+}

exercises/difference-of-squares/src/test/java/DifferenceTest.java

@@ -0,0 +1,87 @@
+import org.junit.Ignore;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public final class DifferenceTest {
+
+    @Test
+    public void testSquareOfSum5() {
+        final int expected = 225;
+        final int actual = Difference.computeSquareOfSumTo(5);
+        assertEquals(expected, actual);
+    }
+
+    @Ignore
+    @Test
+    public void testSquareOfSum10() {
+        final int expected = 3025;
+        final int actual = Difference.computeSquareOfSumTo(10);
+        assertEquals(expected, actual);
+    }
+
+    @Ignore
+    @Test
+    public void testSquareOfSum100() {
+        final int expected = 25502500;
+        final int actual = Difference.computeSquareOfSumTo(100);
+        assertEquals(expected, actual);
+    }
+
+    @Ignore
+    @Test
+    public void testSumOfSquares5() {
+        final int expected = 55;
+        final int actual = Difference.computeSumOfSquaresTo(5);
+        assertEquals(expected, actual);
+    }
+
+    @Ignore
+    @Test
+    public void testSumOfSquares10() {
+        final int expected = 385;
+        final int actual = Difference.computeSumOfSquaresTo(10);
+        assertEquals(expected, actual);
+    }
+
+    @Ignore
+    @Test
+    public void testSumOfSquares100() {
+        final int expected = 338350;
+        final int actual = Difference.computeSumOfSquaresTo(100);
+        assertEquals(expected, actual);
+    }
+
+    @Ignore
+    @Test
+    public void testDifferenceOfSquares0() {
+        final int expected = 0;
+        final int actual = Difference.betweenSquareOfSumAndSumOfSquaresTo(0);
+        assertEquals(expected, actual);
+    }
+
+    @Ignore
+    @Test
+    public void testDifferenceOfSquares5() {
+        final int expected = 170;
+        final int actual = Difference.betweenSquareOfSumAndSumOfSquaresTo(5);
+        assertEquals(expected, actual);
+    }
+
+    @Ignore
+    @Test
+    public void testDifferenceOfSquares10() {
+        final int expected = 2640;
+        final int actual = Difference.betweenSquareOfSumAndSumOfSquaresTo(10);
+        assertEquals(expected, actual);
+    }
+
+    @Ignore
+    @Test
+    public void testDifferenceOfSquares100() {
+        final int expected = 25164150;
+        final int actual = Difference.betweenSquareOfSumAndSumOfSquaresTo(100);
+        assertEquals(expected, actual);
+    }
+
+}

exercises/settings.gradle

@@ -7,6 +7,7 @@ include 'beer-song'
 include 'binary'
 include 'bob'
 include 'crypto-square'
+include 'difference-of-squares'
 include 'etl'
 include 'gigasecond'
 include 'grade-school'