Add the challenge to reverse a string recursively

Author: Geektimus

README.md

@@ -41,4 +41,8 @@ integers. This collection will include the start and end integers if they are od
 We need to write a function that will tell us if all the characters on a given string are unique.
 
 ### Check permutation
-We need to write a function that given two strings let us find if one is a permutation of the other.
+We need to write a function that given two strings let us find if one is a permutation of the other.
+
+### Others (Challenges proposed by Friends or Solved on hackatons)
+#### Recursively reverse a string
+Given a string, reverse the characters and return.

src/main/java/com/codingmaniacs/others/StringChallenges.java

@@ -0,0 +1,17 @@
+package com.codingmaniacs.others;
+
+public class StringChallenges {
+    /**
+     * Given a string it reverses the order of the chars
+     *
+     * @param str String
+     * @return String on reverse order
+     */
+    public static String reverse(String str) {
+        if (str.length() == 0) return str;
+        else {
+            int last = str.length() - 1;
+            return str.charAt(last) + reverse(str.substring(0, last));
+        }
+    }
+}

src/test/java/com/codingmaniacs/others/StringChallengesTests.java

@@ -0,0 +1,53 @@
+package com.codingmaniacs.others;
+
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class StringChallengesTests {
+
+    @Test
+    public void reverseRecursiveEmptyString() {
+        String str = "";
+        String expected = "";
+
+        String result = StringChallenges.reverse(str);
+        assertEquals("The reverse of an empty string is the same empty string", expected, result);
+    }
+
+    @Test
+    public void reverseRecursiveSingleCharString() {
+        String str = "a";
+        String expected = "a";
+
+        String result = StringChallenges.reverse(str);
+        assertEquals("The reverse of a single char is the same char", expected, result);
+    }
+
+    @Test
+    public void reverseRecursiveAB() {
+        String str = "ab";
+        String expected = "ba";
+
+        String result = StringChallenges.reverse(str);
+        assertEquals("The reverse of ab is ba", expected, result);
+    }
+
+    @Test
+    public void reverseRecursiveMultipleRepetitions() {
+        String str = "aaa";
+        String expected = "aaa";
+
+        String result = StringChallenges.reverse(str);
+        assertEquals("The reverse of aaa is aaa", expected, result);
+    }
+
+    @Test
+    public void reverseRecursiveComplexString() {
+        String str = "longer and complex words";
+        String expected = "sdrow xelpmoc dna regnol";
+
+        String result = StringChallenges.reverse(str);
+        assertEquals("The reverse of an empty string is the same empty string", expected, result);
+    }
+}