add merge sort

Author: Hopson97

build.gradle

@@ -4,27 +4,14 @@ apply plugin: 'application'
 sourceCompatibility = '1.8'
 [compileJava, compileTestJava]*.options*.encoding = 'UTF-8'
 
-// NetBeans will automatically add "run" and "debug" tasks relying on the
-// "mainClass" property. You may however define the property prior executing
-// tasks by passing a "-PmainClass=<QUALIFIED_CLASS_NAME>" argument.
-//
-// Note however, that you may define your own "run" and "debug" task if you
-// prefer. In this case NetBeans will not add these tasks but you may rely on
-// your own implementation.
 if (!hasProperty('mainClass')) {
     ext.mainClass = 'sortVisualiser.SortVisualiser'
 }
 
 repositories {
     mavenCentral()
-    // You may define additional repositories, or even remove "mavenCentral()".
-    // Read more about repositories here:
-    //   http://www.gradle.org/docs/current/userguide/dependency_management.html#sec:repositories
 }
 
 dependencies {
-    // TODO: Add dependencies here ...
-    // You can read more about how to add dependency here:
-    //   http://www.gradle.org/docs/current/userguide/dependency_management.html#sec:how_to_declare_your_dependencies
     testCompile group: 'junit', name: 'junit', version: '4.10'
 }

src/main/java/sortVisualiser/SortVisualiser.java

@@ -5,6 +5,7 @@
 import sortVisualiser.algorithms.BubbleSort;
 import sortVisualiser.algorithms.ISortAlgorithm;
 import sortVisualiser.algorithms.InsertionSort;
+import sortVisualiser.algorithms.MergeSort;
 import sortVisualiser.algorithms.QuickSort;
 import sortVisualiser.algorithms.SelectionSort;
 import static util.Sleep.secondsToNano;
@@ -32,10 +33,11 @@ public SortVisualiser() {
         window.setVisible(true);
 
         sortQueue = new ArrayList<>();
-        sortQueue.add(new QuickSort());
-        sortQueue.add(new SelectionSort());
-        sortQueue.add(new InsertionSort());
-        sortQueue.add(new BubbleSort());
+        sortQueue.add(new MergeSort());
+        //sortQueue.add(new QuickSort());
+        //sortQueue.add(new SelectionSort());
+        //sortQueue.add(new InsertionSort());
+        //sortQueue.add(new BubbleSort());
     }
 
     private void shuffleAndWait() {

src/main/java/sortVisualiser/algorithms/InsertionSort.java

@@ -30,5 +30,4 @@ public String getName() {
     public long getDelay() {
         return 2;
     }
-
 }

src/main/java/sortVisualiser/algorithms/MergeSort.java

@@ -0,0 +1,83 @@
+package sortVisualiser.algorithms;
+
+import sortVisualiser.SortArray;
+
+/**
+ *  Merge sort implementation
+ * @author Matthew Hopson
+ */
+public class MergeSort implements ISortAlgorithm
+{
+    private int[] getSubArray(SortArray array, int begin, int size) {
+        int arr[] = new int[size];
+        for (int i = 0; i < size; i++) {
+            arr[i] = array.getValue(begin + i);
+        }
+        return arr;
+    }
+    
+    private void merge(SortArray array, int left, int middle, int right) {
+        //Size of the left and right "sub arrays"
+        int leftSize = middle - left + 1;
+        int rightSize = right - middle;
+        
+        int leftArray[]  = getSubArray(array, left, leftSize);
+        int rightArray[] = getSubArray(array, middle + 1, rightSize);
+        
+        int i = 0, j = 0, k = left;
+        while (i < leftSize && j < rightSize) {
+            if (leftArray[i] <= rightArray[j]) {
+                array.updateSingle(k, leftArray[i], getDelay());
+                i++;
+            }
+            else {
+                array.updateSingle(k, rightArray[j], getDelay());
+                j++;
+            }
+            k++;
+        }
+        //remaining stufffff
+        while (i < leftSize) {
+            array.updateSingle(k, leftArray[i], getDelay());
+            i++;
+            k++;
+        }
+        while (j < rightSize) {
+            array.updateSingle(k, rightArray[j], getDelay());
+            j++;
+            k++;
+        }
+    }
+    
+    private void mergeSort(SortArray array, int left, int right) {
+        if (left < right) {
+            int middleIndex = (left + right) / 2;
+            
+            //Merge sort is a "divide and conquer" algorithm
+            //It works by splitting the array into tiny sections 
+            //and sorting them indivually,
+            //and then finally merges it back together
+            mergeSort(array, left, middleIndex);
+            mergeSort(array, middleIndex + 1, right);
+            
+            merge(array, left, middleIndex, right);
+        }
+    }
+    
+    @Override
+    public void runSort(SortArray array) {
+        int left = 0;
+        int right = array.arraySize() - 1;
+        mergeSort(array, left, right);
+    }
+
+    @Override
+    public String getName() {
+        return "Merge Sort";
+    }
+
+    @Override
+    public long getDelay() {
+        return 10;
+    }
+}

src/main/java/sortVisualiser/algorithms/SelectionSort.java

@@ -10,9 +10,10 @@ public class SelectionSort implements ISortAlgorithm
 {
     @Override
     public void runSort(SortArray array) {
-        for (int i = 0; i < array.arraySize() - 1; i++) {
+        int len = array.arraySize();
+        for (int i = 0; i < len - 1; i++) {
             int minIndex = i;
-            for (int j = i + 1; j < array.arraySize(); j++) {
+            for (int j = i + 1; j < len; j++) {
                 if (array.getValue(j) < array.getValue(minIndex)) {
                     minIndex = j;
                 }