Implement Quicksort

QuickSort/.gitignore

@@ -0,0 +1 @@
+bin/

QuickSort/src/lab/QuickSort.java

@@ -13,5 +13,33 @@ public abstract class QuickSort {
 	public abstract void Quicksort(SortArray records, int left, int right);
 
 	// You may add additional methods here
+	protected int partition(SortingItem pivot, SortArray records, int leftBound, int rightBound) {
+		
+		if(leftBound == rightBound)
+			return leftBound;
+		
+		int leftIndex = leftBound;
+		int rightIndex = rightBound;
+		
+		while(true){
+			while(leftIndex < rightBound && records.getElementAt(leftIndex).compareTo(pivot) < 0) {
+				leftIndex += 1;
+			}
+			while(rightIndex > leftBound && records.getElementAt(rightIndex).compareTo(pivot) > 0) {
+				rightIndex -= 1;
+			}
+			if(leftIndex >= rightIndex) {
+				return rightIndex;
+			}
+			
+			swap(leftIndex, rightIndex, records);
+		}
+	}
+	
+	protected void swap(int i1, int i2, SortArray records) {
+		SortingItem temp = records.getElementAt(i1);
+		records.setElementAt(i1, records.getElementAt(i2));
+		records.setElementAt(i2, temp);
+	}
 
 }

QuickSort/src/lab/QuickSortA.java

@@ -18,11 +18,16 @@ public class QuickSortA extends QuickSort {
 	 */
 	@Override
 	public void Quicksort(SortArray records, int left, int right) {
-		// TODO
 		// implement the Quicksort A algorithm to sort the records
 		// (choose the pivot as the first (leftmost) element in the list)
+		
+		if(right - left < 1)
+			return;
+		
+		SortingItem pivot = records.getElementAt(left);
+		int p = partition(pivot, records, left, right);
+		Quicksort(records, left, p);
+		Quicksort(records, p+1, right);
 	}
 
-	// You may add additional methods here
-
 }

QuickSort/src/lab/QuickSortB.java

@@ -18,12 +18,39 @@ public class QuickSortB extends QuickSort {
 	 */
 	@Override
 	public void Quicksort(SortArray records, int left, int right) {
-		// TODO
 		// implement the Quicksort B algorithm to sort the records
 		// (choose the pivot as the median value of the elements at position
 		// (left (first),middle,right(last)))
+		if(right - left < 1)
+			return;
+		
+		SortingItem pivot = getPivot(left, right, records);
+		int p = partition(pivot, records, left, right);
+		Quicksort(records, left, p);
+		Quicksort(records, p+1, right);
+	}
+	
+	private SortingItem getPivot(int left, int right, SortArray records) {
+		SortingItem l = records.getElementAt(left);
+		SortingItem r = records.getElementAt(right);
+		SortingItem m = records.getElementAt((int) Math.floor(left + (right - left) / 2));
+		SortingItem t = null;
+		
+		// 'Sort' the three elements by doing two swaps if necessary, then return the middle (= median) one
+		
+		if(l.compareTo(m) > 0) {
+			t = l;
+			l = m;
+			m = t;
+		}
+		
+		if(r.compareTo(m) < 0) {
+			t = r;
+			r = m;
+			m = t;
+		}
+		
+		return m;
 	}
 
-	// You may add additional methods here
-
 }

QuickSort/src/lab/SortingItem.java

@@ -5,7 +5,7 @@ package lab;
  * This class represents one entry of the list that has to be sorted.
  * 
  */
-public class SortingItem {
+public class SortingItem implements Comparable<SortingItem>{
 
 	// DO NOT modify
 	public String BookSerialNumber;
@@ -24,6 +24,9 @@ public class SortingItem {
 		this.Status = otherItem.Status;
 	}
 
-	// You may add additional methods here
+	@Override
+	public int compareTo(SortingItem arg0) {
+		return this.BookSerialNumber.compareTo(arg0.BookSerialNumber) == 0 ? this.ReaderID.compareTo(arg0.ReaderID): this.BookSerialNumber.compareTo(arg0.BookSerialNumber);
+	}
 
 }