From 64dd6b66932fff90efecc8150917f470a52b4bb7 Mon Sep 17 00:00:00 2001
From: jrtechs <jeffery@jrtechs.net>
Date: Mon, 27 Aug 2018 21:59:30 -0400
Subject: [PATCH] Implemented merge sort using my custom array list.

---
 .../net/jrtechs/www/Sorting/MergeSort.java    | 101 ++++++++++++++++++
 .../net/jrtechs/www/Sorting/SortableList.java |   1 +
 .../jrtechs/www/sorting/MergeSortTest.java    |  50 +++++++++
 3 files changed, 152 insertions(+)
 create mode 100644 src/main/java/net/jrtechs/www/Sorting/MergeSort.java
 create mode 100644 src/test/java/net/jrtechs/www/sorting/MergeSortTest.java

diff --git a/src/main/java/net/jrtechs/www/Sorting/MergeSort.java b/src/main/java/net/jrtechs/www/Sorting/MergeSort.java
new file mode 100644
index 0000000..4c053f0
--- /dev/null
+++ b/src/main/java/net/jrtechs/www/Sorting/MergeSort.java
@@ -0,0 +1,101 @@
+package net.jrtechs.www.Sorting;
+
+import net.jrtechs.www.DataStructures.Lists.ArrayList.ArrayBackedList;
+
+
+/**
+ * Object used to sort lists
+ *
+ * @author Jeffery Russell 8-27-18
+ * @param <E>
+ */
+public class MergeSort<E extends Comparable>
+{
+    /** Constant for an increasing list */
+    public static final int INCREASING_ORDER = 1;
+
+    /** Constant for a decreasing list */
+    public static final int DECREASING_ORDER = -1;
+
+    /** Type of ordering*/
+    private int sortType;
+
+
+    /**
+     * Creates a new sorter with a specific ordering
+     *
+     * @param sortType sorting constant
+     */
+    public MergeSort(int sortType)
+    {
+        this.sortType= sortType;
+    }
+
+
+    /**
+     * Divides and conquer approach to sorting an array
+     *
+     * @param list list to sort
+     * @return sorted list
+     */
+    public ArrayBackedList<E> mergeSort(ArrayBackedList<E> list)
+    {
+        if(list.size() <= 1)
+            return list;
+
+        ArrayBackedList<E> left = new ArrayBackedList<>(list.size()/2);
+        ArrayBackedList<E> right = new ArrayBackedList<>(list.size()/2);
+
+
+        for(int i = 0; i < list.size()/2; i++)
+        {
+            left.add(list.get(i));
+        }
+        for(int i = list.size()/2; i< list.size(); i++)
+        {
+            right.add(list.get(i));
+        }
+
+        left = mergeSort(left);
+        right = mergeSort(right);
+
+        return mergeLists(left, right);
+    }
+
+
+    /**
+     * Merges two ordered lists together in a way in which produces
+     * another ordered list.
+     *
+     * @param left ordered list
+     * @param right ordered list
+     * @return ordered list
+     */
+    private SortableList<E> mergeLists(ArrayBackedList<E> left,
+                               ArrayBackedList<E> right)
+    {
+        SortableList<E> result = new SortableList<>
+                (left.size() + right.size());
+
+        //Trick I did because the remove operation of the
+        //arraybackedList is not O(N)
+        int rightRemoved = 0, leftRemoved = 0;
+
+        while(left.size() != leftRemoved && right.size() != rightRemoved)
+        {
+            if(left.get(leftRemoved).compareTo(right.get(rightRemoved))
+                    != this.sortType)
+                result.add(left.get(leftRemoved++));
+            else
+                result.add(right.get(rightRemoved++));
+        }
+
+        while(left.size() != leftRemoved)
+            result.add(left.get(leftRemoved++));
+
+        while(right.size() != rightRemoved)
+            result.add(right.get(rightRemoved++));
+
+        return result;
+    }
+}
diff --git a/src/main/java/net/jrtechs/www/Sorting/SortableList.java b/src/main/java/net/jrtechs/www/Sorting/SortableList.java
index 591887a..58727d4 100644
--- a/src/main/java/net/jrtechs/www/Sorting/SortableList.java
+++ b/src/main/java/net/jrtechs/www/Sorting/SortableList.java
@@ -55,4 +55,5 @@ public class SortableList<E extends Comparable> extends ArrayBackedList<E>
             }
         }
     }
+
 }
diff --git a/src/test/java/net/jrtechs/www/sorting/MergeSortTest.java b/src/test/java/net/jrtechs/www/sorting/MergeSortTest.java
new file mode 100644
index 0000000..a9d8953
--- /dev/null
+++ b/src/test/java/net/jrtechs/www/sorting/MergeSortTest.java
@@ -0,0 +1,50 @@
+package net.jrtechs.www.sorting;
+
+import net.jrtechs.www.DataStructures.Lists.ArrayList.ArrayBackedList;
+import net.jrtechs.www.Sorting.MergeSort;
+import org.junit.Test;
+
+import static junit.framework.TestCase.assertNotNull;
+import static junit.framework.TestCase.assertTrue;
+
+public class MergeSortTest
+{
+    @Test
+    public void testInitalization()
+    {
+        MergeSort<Double> sorter = new MergeSort<>(MergeSort.DECREASING_ORDER);
+
+        assertNotNull(sorter);
+    }
+
+
+    @Test
+    public void testInsertionSortAscending()
+    {
+        MergeSort<Double> sorter = new MergeSort<>(MergeSort.INCREASING_ORDER);
+        ArrayBackedList<Double> list = new ArrayBackedList<>();
+        list.add(1.0);
+        list.add(0.0);
+        list.add(3.0);
+        list.add(-12.0);
+        list = sorter.mergeSort(list);
+
+        assertTrue(list.get(0) == -12.0);
+        assertTrue(list.get(list.size() -1) == 3);
+    }
+
+    @Test
+    public void testInsertionSortDescending()
+    {
+        MergeSort<Double> sorter = new MergeSort<>(MergeSort.DECREASING_ORDER);
+        ArrayBackedList<Double> list = new ArrayBackedList<>();
+        list.add(1.2);
+        list.add(1.0);
+        list.add(0.0);
+        list.add(3.0);
+        list.add(-12.0);
+        list = sorter.mergeSort(list);
+        assertTrue(list.get(0) == 3.0);
+        assertTrue(list.get(list.size() -1) == -12);
+    }
+}