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95 lines
2.1 KiB
95 lines
2.1 KiB
package net.jrtechs.www.Sorting;
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import net.jrtechs.www.DataStructures.Lists.ArrayList.ArrayBackedList;
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import java.util.Random;
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/**
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* Basic implementation of quick sort in java.
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*
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* @author Jeffery Russell
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* @param <E>
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*/
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public class QuickSort<E extends Comparable>
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{
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/** Constant for an increasing list */
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public static final int INCREASING_ORDER = 1;
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/** Constant for a decreasing list */
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public static final int DECREASING_ORDER = -1;
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/** Type of ordering*/
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private int sortType;
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/**
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* Creates a new sorter with a specific ordering
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*
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* @param sortType sorting constant
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*/
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public QuickSort(int sortType)
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{
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this.sortType= sortType;
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}
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/**
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* Wrapper function for initial call.
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*
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* @param list
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*/
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public void quickSort(ArrayBackedList<E> list)
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{
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quickSort(list, 0, list.size() -1);
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}
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/**
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* Quick sorts the array.
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*
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* @param list array to sort
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* @param left left index
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* @param right right index
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*/
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public void quickSort(ArrayBackedList<E> list, int left, int right)
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{
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if(left < right)
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{
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int pivot = partition(list, left, right);
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quickSort(list, left, pivot -1);
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quickSort(list, pivot + 1, right);
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}
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}
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/**
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* Selects a random pivot and swaps everything less than the pivot value
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* to the left and everything greater than the pivot to the right.
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*
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* @param list array list to sort
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* @param left left index
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* @param right right index
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* @return index of the sorted part
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*/
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private int partition(ArrayBackedList<E> list, int left, int right)
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{
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Random random = new Random();
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int p = random.nextInt((right - left) + 1) + left; //select pivot
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list.swap(p, right);
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int store = left;
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for(int i = left; i < right; i++)
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{
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if(list.get(i).compareTo(list.get(right)) != this.sortType)
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{
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list.swap(i, store);
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store++;
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}
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}
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list.swap(store, right);
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return store;
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}
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}
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