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101 lines
2.5 KiB
101 lines
2.5 KiB
package net.jrtechs.www.Sorting;
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import net.jrtechs.www.DataStructures.Lists.ArrayList.ArrayBackedList;
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/**
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* Object used to sort lists
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*
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* @author Jeffery Russell 8-27-18
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* @param <E>
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*/
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public class MergeSort<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 MergeSort(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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* Divides and conquer approach to sorting an array
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*
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* @param list list to sort
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* @return sorted list
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*/
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public ArrayBackedList<E> mergeSort(ArrayBackedList<E> list)
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{
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if(list.size() <= 1)
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return list;
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ArrayBackedList<E> left = new ArrayBackedList<>(list.size()/2);
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ArrayBackedList<E> right = new ArrayBackedList<>(list.size()/2);
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for(int i = 0; i < list.size()/2; i++)
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{
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left.add(list.get(i));
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}
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for(int i = list.size()/2; i< list.size(); i++)
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{
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right.add(list.get(i));
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}
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left = mergeSort(left);
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right = mergeSort(right);
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return mergeLists(left, right);
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}
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/**
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* Merges two ordered lists together in a way in which produces
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* another ordered list.
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*
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* @param left ordered list
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* @param right ordered list
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* @return ordered list
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*/
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private SortableList<E> mergeLists(ArrayBackedList<E> left,
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ArrayBackedList<E> right)
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{
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SortableList<E> result = new SortableList<>
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(left.size() + right.size());
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//Trick I did because the remove operation of the
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//arraybackedList is not O(N)
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int rightRemoved = 0, leftRemoved = 0;
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while(left.size() != leftRemoved && right.size() != rightRemoved)
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{
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if(left.get(leftRemoved).compareTo(right.get(rightRemoved))
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!= this.sortType)
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result.add(left.get(leftRemoved++));
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else
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result.add(right.get(rightRemoved++));
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}
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while(left.size() != leftRemoved)
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result.add(left.get(leftRemoved++));
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while(right.size() != rightRemoved)
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result.add(right.get(rightRemoved++));
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return result;
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}
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}
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