Added triangle exercise (see #3)

config.json

@@ -15,7 +15,8 @@
     "phone-number",
     "grade-school",
     "space-age",
-    "gigasecond"
+    "gigasecond",
+    "triangle"
   ],
   "deprecated": [
   ],

triangle/build.gradle

@@ -0,0 +1,11 @@
+apply plugin: "java"
+apply plugin: "eclipse"
+apply plugin: "idea"
+
+repositories {
+  mavenCentral()
+}
+
+dependencies {
+  testCompile "junit:junit:4.10"
+}

triangle/example.java

@@ -0,0 +1,53 @@
+public class Triangle {
+
+    private double side1;
+    private double side2;
+    private double side3;
+
+    public Triangle(double side1, double side2, double side3) throws TriangleException {
+        this.side1 = side1;
+        this.side2 = side2;
+        this.side3 = side3;
+
+        if (allSidesAreZero() || hasImpossibleSides() || violatesTriangleInequality()) {
+            throw new TriangleException();
+        }
+    }
+
+    public TriangleKind getKind() {
+        int uniqueSides = getNumberOfUniqueSides();
+
+        if (uniqueSides == 1) {
+            return TriangleKind.EQUILATERAL;
+        }
+
+        if (uniqueSides == 2) {
+            return TriangleKind.ISOSCELES;
+        }
+
+        return TriangleKind.SCALENE;
+    }
+
+    private boolean allSidesAreZero() {
+        return side1 == 0 && side2 == 0 && side3 == 0;
+    }
+
+    private boolean hasImpossibleSides() {
+        return side1 < 0 || side2 < 0 || side3 < 0;
+    }
+
+    private boolean violatesTriangleInequality() {
+        return side1 + side2 <= side3 || side1 + side3 <= side2 || side2 + side3 <= side1;
+    }
+
+
+    public int getNumberOfUniqueSides() {
+        Set<Double> sides = new HashSet<>();
+
+        sides.add(side1);
+        sides.add(side2);
+        sides.add(side3);
+
+        return sides.size();
+    }
+}

triangle/src/main/java/Triangle.java

@@ -0,0 +1,2 @@
+public class Triangle {
+}

triangle/src/main/java/TriangleException.java

@@ -0,0 +1,5 @@
+public class TriangleException extends Exception {
+
+    public TriangleException() {
+    }
+}

triangle/src/main/java/TriangleKind.java

@@ -0,0 +1,5 @@
+public enum TriangleKind {
+    EQUILATERAL,
+    ISOSCELES,
+    SCALENE
+}

triangle/src/test/java/TriangleTest.java

@@ -0,0 +1,101 @@
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class TriangleTest {
+
+    @Test
+    public void equilateralTriangleHaveEqualSides() throws Exception {
+        Triangle triangle = new Triangle(2, 2, 2);
+
+        assertEquals(triangle.getKind(), TriangleKind.EQUILATERAL);
+    }
+
+    @Test
+    public void largerEquilateralTrianglesAlsoHaveEqualSides() throws Exception {
+        Triangle triangle = new Triangle(10, 10, 10);
+
+        assertEquals(triangle.getKind(), TriangleKind.EQUILATERAL);
+    }
+
+    @Test
+    public void isoscelesTrianglesHaveLastTwoSidesEqual() throws Exception {
+        Triangle triangle = new Triangle(3, 4, 4);
+
+        assertEquals(triangle.getKind(), TriangleKind.ISOSCELES);
+    }
+
+    @Test
+    public void isoscelesTrianglesHaveFirstAndLastSidesEqual() throws Exception {
+        Triangle triangle = new Triangle(4, 3, 4);
+
+        assertEquals(triangle.getKind(), TriangleKind.ISOSCELES);
+    }
+
+    @Test
+    public void isoscelesTrianglesHaveTwoFirstSidesEqual() throws Exception {
+        Triangle triangle = new Triangle(4, 4, 3);
+
+        assertEquals(triangle.getKind(), TriangleKind.ISOSCELES);
+    }
+
+    @Test
+    public void isoscelesTrianglesHaveInFactExactlyTwoSidesEqual() throws Exception {
+        Triangle triangle = new Triangle(10, 10, 2);
+
+        assertEquals(triangle.getKind(), TriangleKind.ISOSCELES);
+    }
+
+    @Test
+    public void scaleneTrianglesHaveNoEqualSides() throws Exception {
+        Triangle triangle = new Triangle(3, 4, 5);
+
+        assertEquals(triangle.getKind(), TriangleKind.SCALENE);
+    }
+
+    @Test
+    public void scaleneTrianglesHaveNoEqualSidesAtLargerScaleEither() throws Exception {
+        Triangle triangle = new Triangle(10, 11, 12);
+
+        assertEquals(triangle.getKind(), TriangleKind.SCALENE);
+    }
+
+    @Test
+    public void scaleneTrianglesHaveNoEqualSidesInDescendingOrderEither() throws Exception {
+        Triangle triangle = new Triangle(5, 4, 2);
+
+        assertEquals(triangle.getKind(), TriangleKind.SCALENE);
+    }
+
+    @Test
+    public void verySmallTrianglesAreLegal() throws Exception {
+        Triangle triangle = new Triangle(0.4, 0.6, 0.3);
+
+        assertEquals(triangle.getKind(), TriangleKind.SCALENE);
+    }
+
+    @Test(expected = TriangleException.class)
+    public void trianglesWithNoSizeAreIllegal() throws Exception {
+        new Triangle(0, 0, 0);
+    }
+
+    @Test(expected = TriangleException.class)
+    public void trianglesWithNegativeSidesAreIllegal() throws Exception {
+        new Triangle(3, 4, -5);
+    }
+
+    @Test(expected = TriangleException.class)
+    public void trianglesViolatingTriangleInequalityAreIllegal() throws Exception {
+        new Triangle(1, 1, 3);
+    }
+
+    @Test(expected = TriangleException.class)
+    public void trianglesViolatingTriangleInequalityAreIllegal2() throws Exception {
+        new Triangle(2, 4, 2);
+    }
+
+    @Test(expected = TriangleException.class)
+    public void trianglesViolatingTriangleInequalityAreIllegal3() throws Exception {
+        new Triangle(7, 3, 2);
+    }
+}