Added MapReduce Algorithm in Misc Folder. (#4828)

* Added MapReduce Algorithm in Misc Folder.

* Did formatting correctly

* Removed main function and added MapReduceTest

* format the code

src/test/java/com/thealgorithms/misc/MapReduceTest.java

@@ -0,0 +1,23 @@
+package com.thealgorithms.misc;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import org.junit.jupiter.api.Test;
+
+public class MapReduceTest {
+    @Test
+    public void testMapReduceWithSingleWordSentence() {
+        String oneWordSentence = "Hactober";
+        String result = MapReduce.mapreduce(oneWordSentence);
+
+        assertEquals("Hactober: 1", result);
+    }
+
+    @Test
+    public void testMapReduceWithMultipleWordSentence() {
+        String multipleWordSentence = "I Love Love HactoberFest";
+        String result = MapReduce.mapreduce(multipleWordSentence);
+
+        assertEquals("I: 1,Love: 2,HactoberFest: 1", result);
+    }
+}