Added exercise atbash-cipher

atbash-cipher/build.gradle

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

atbash-cipher/example.java

@@ -0,0 +1,48 @@
+import java.util.ArrayList;
+import java.util.List;
+
+public class Atbash {
+
+    private static final int GROUP_SIZE = 5;
+    private static final String PLAIN = "abcdefghijklmnopqrstuvwxyz";
+    private static final String CIPHER = "zyxwvutsrqponmlkjihgfedcba";
+
+    public static String encode(String input) {
+        String encoded = stripInvalidCharacters(input).toLowerCase();
+        String cyphered = "";
+
+        for (char c : encoded.toCharArray()) {
+            cyphered += applyCipher(c);
+        }
+
+        return splitIntoFiveLetterWords(cyphered);
+    }
+
+    private static String stripInvalidCharacters(String input) {
+        String filteredValue = "";
+
+        for (char c : input.toCharArray()) {
+            if (Character.isLetterOrDigit(c)) {
+                filteredValue += c;
+            }
+        }
+
+        return filteredValue;
+    }
+
+    private static char applyCipher(char input) {
+        int idx = PLAIN.indexOf(input);
+
+        return idx >= 0 ? CIPHER.toCharArray()[idx] : input;
+    }
+
+    private static String splitIntoFiveLetterWords(String value) {
+        List<String> words = new ArrayList<>();
+
+        for (int i = 0; i < value.length(); i += GROUP_SIZE) {
+            words.add(i + GROUP_SIZE <= value.length() ? value.substring(i, i + GROUP_SIZE) : value.substring(i));
+        }
+
+        return String.join(" ", words);
+    }
+}

atbash-cipher/src/main/java/Atbash.java

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

atbash-cipher/src/test/java/AtbashTest.java

@@ -0,0 +1,38 @@
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.Parameterized;
+
+import java.util.Arrays;
+import java.util.Collection;
+
+import static org.junit.Assert.assertEquals;
+
+@RunWith(Parameterized.class)
+public class AtbashTest {
+
+    private String input;
+    private String expectedOutput;
+
+    @Parameterized.Parameters
+    public static Collection<Object[]> data() {
+        return Arrays.asList(new Object[][]{
+                {"no", "ml"},
+                {"yes", "bvh"},
+                {"OMG", "lnt"},
+                {"mindblowingly", "nrmwy oldrm tob"},
+                {"Testing, 1 2 3, testing.", "gvhgr mt123 gvhgr mt"},
+                {"Truth is fiction.", "gifgs rhurx grlm"},
+                {"The quick brown fox jumps over the lazy dog.", "gsvjf rxpyi ldmul cqfnk hlevi gsvoz abwlt"}
+        });
+    }
+
+    public AtbashTest(String input, String expectedOutput) {
+        this.input = input;
+        this.expectedOutput = expectedOutput;
+    }
+
+    @Test
+    public void test() {
+        assertEquals(expectedOutput, Atbash.encode(input));
+    }
+}

config.json

@@ -23,7 +23,8 @@
     "prime-factors",
     "raindrops",
     "allergies",
-    "strain"
+    "strain",
+    "atbash-cipher"
   ],
   "deprecated": [
   ],