Added partial array reverse

Author: viktor-podzigun

src/main/java/algorithms/array/ReverseArray.java

@@ -3,7 +3,11 @@
 public class ReverseArray {
 
     public static int[] reverse(int[] arr) {
-        for (int i = 0, j = arr.length - 1; i < j; i++, j--) {
+        return reverse(arr, 0, arr.length);
+    }
+    
+    public static int[] reverse(int[] arr, int offset, int length) {
+        for (int i = offset, j = offset + length - 1; i < j; i++, j--) {
             int tmp = arr[i];
             arr[i] = arr[j];
             arr[j] = tmp;

src/test/scala/algorithms/array/ReverseArraySpec.scala

@@ -1,17 +1,27 @@
 package algorithms.array
 
+import algorithms.array.ReverseArray._
 import org.scalatest.{FlatSpec, Matchers}
 
 class ReverseArraySpec extends FlatSpec with Matchers {
 
   it should "reverse the whole array" in {
-    //given
-    val arr = Array(1, 2, 3, 4, 5)
-    
-    //when
-    val result = ReverseArray.reverse(arr)
-    
-    //then
-    result.toList shouldBe List(5, 4, 3, 2, 1)
+    //when & then
+    reverse(Array.empty[Int]).toList shouldBe Nil
+    reverse(Array(1)).toList shouldBe List(1)
+    reverse(Array(1, 2)).toList shouldBe List(2, 1)
+    reverse(Array(1, 2, 3, 4, 5)).toList shouldBe List(5, 4, 3, 2, 1)
+  }
+  
+  it should "reverse part of the array" in {
+    //when & then
+    reverse(Array(1, 2, 3, 4, 5, 6, 7), 0, 0).toList shouldBe List(1, 2, 3, 4, 5, 6, 7)
+    reverse(Array(1, 2, 3, 4, 5, 6, 7), 0, 1).toList shouldBe List(1, 2, 3, 4, 5, 6, 7)
+    reverse(Array(1, 2, 3, 4, 5, 6, 7), 0, 2).toList shouldBe List(2, 1, 3, 4, 5, 6, 7)
+    reverse(Array(1, 2, 3, 4, 5, 6, 7), 0, 3).toList shouldBe List(3, 2, 1, 4, 5, 6, 7)
+    reverse(Array(1, 2, 3, 4, 5, 6, 7), 1, 2).toList shouldBe List(1, 3, 2, 4, 5, 6, 7)
+    reverse(Array(1, 2, 3, 4, 5, 6, 7), 1, 4).toList shouldBe List(1, 5, 4, 3, 2, 6, 7)
+    reverse(Array(1, 2, 3, 4, 5, 6, 7), 5, 2).toList shouldBe List(1, 2, 3, 4, 5, 7, 6)
+    reverse(Array(1, 2, 3, 4, 5, 6, 7), 6, 0).toList shouldBe List(1, 2, 3, 4, 5, 6, 7)
   }
 }