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QuickSort.java
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QuickSort.java
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/*
* Copyright 2020 Emory University
*
* 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
*
* http://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.
*/
package edu.emory.cs.sort.divide_conquer;
import edu.emory.cs.sort.AbstractSort;
import java.util.Comparator;
/**
* @author Jinho D. Choi ({@code jinho.choi@emory.edu})
*/
public class QuickSort<T extends Comparable<T>> extends AbstractSort<T> {
public QuickSort() {
this(Comparator.naturalOrder());
}
public QuickSort(Comparator<T> comparator) {
super(comparator);
}
@Override
public void sort(T[] array, int beginIndex, int endIndex) {
// at least one key in the range
if (beginIndex >= endIndex) return;
int pivotIndex = partition(array, beginIndex, endIndex);
// sort left partition
sort(array, beginIndex, pivotIndex);
// sort right partition
sort(array, pivotIndex + 1, endIndex);
}
protected int partition(T[] array, int beginIndex, int endIndex) {
int fst = beginIndex, snd = endIndex;
while (true) {
// find where endIndex > fst > pivot
while (++fst < endIndex && compareTo(array, beginIndex, fst) >= 0);
// find where beginIndex < snd < pivot
while (--snd > beginIndex && compareTo(array, beginIndex, snd) <= 0);
// pointers crossed
if (fst >= snd) break;
// exchange
swap(array, fst, snd);
}
swap(array, beginIndex, snd);
return snd;
}
}