OOP2

/* opdracht3.java - Opdracht 3 of OOP2, generic typing.

 Copyright 2015 Maarten Vangeneugden

	Licensed under the Apache License, Version 2.0 (the "License");

	you may not use this file except in compliance with the License.

	You may obtain a copy of the License at

	https://www.apache.org/licenses/LICENSE-2.0

	Unless required by applicable law or agreed to in writing, software

	distributed under the License is distributed on an "AS IS" BASIS,

	WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

	See the License for the specific language governing permissions and

	limitations under the License.*/

import java.util.ArrayList;

import java.util.Random;

class ItHurtsWhenIP {

		/** Sorts a given ArrayList using quicksort.

		 * @param array An ArrayList of items to be sorted.

		 * @return The same ArrayList, but sorted.

		 * @pre The given list is of type ArrayList. The items in the list implement the class Comparable.

		 * @post The items in the list are sorted according to their implementation of Comparable.

		 * @exception NullPointerException Thrown when the given array is not there.

		 */

		public static <T extends Comparable> ArrayList<T> quickSort(ArrayList<T> array) {

				int index = new Random().nextInt(array.size()); // A random pivot between 0 and the size of the array.

				T pivot = array.get(index); // Taking the pivot element.

				if(array.size() == 0 || array.size() == 1) { // If the size of the array is too small to sort, return it as is.

						return array;

				}

				for (T value : array) { // Else, loop trough the elements, and sort them according to the pivot.

					if(value.compareTo(pivot) < 0) { // If the value is smaller than the pivot:

							if(array.indexOf(value) > index) { //If the value comes after the pivot, replace:

									array.set(array.indexOf(value), pivot);

									array.set(index, value);

							}

					}

					else { // The value is greater than the pivot:

							if(array.indexOf(value) < index) { // If the value comes before the pivot, replace:

									array.set(array.indexOf(value), pivot);

									array.set(index, value);

							}

					}

				}

				if(array.size() == 2 || array.size() == 3) // If the array is only 2 or 3 long, do not go recursive. instead, return it.

						return array;

				else { // If the array needs additional quicksorting, do so:

						ArrayList<T> lowerPart = quickSort((ArrayList)array.subList(0, index)); // Sorting the lower list.

						lowerPart.add(pivot); // Adding the pivot to the sorted lower list.

						ArrayList<T> upperPart = quickSort((ArrayList)array.subList(index, array.size())); // Sorting the upper list.

						lowerPart.addAll(upperPart); // Adding the upper sorted list to the lower sorted list.

						return lowerPart; // Returning it.

				}

		}

}