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QuickSort.java
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QuickSort.java
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/**
* Quicksort implementation using Hoare partitioning
*
* <p>Run with:
*
* <p>$ ./gradlew run -Palgorithm=sorting.QuickSort
*
* @author William Fiset, [email protected]
*/
package com.williamfiset.algorithms.sorting;
public class QuickSort implements InplaceSort {
@Override
public void sort(int[] values) {
QuickSort.quicksort(values);
}
public static void quicksort(int[] ar) {
if (ar == null) return;
quicksort(ar, 0, ar.length - 1);
}
// Sort interval [lo, hi] inplace recursively
private static void quicksort(int[] ar, int lo, int hi) {
if (lo < hi) {
int splitPoint = partition(ar, lo, hi);
quicksort(ar, lo, splitPoint);
quicksort(ar, splitPoint + 1, hi);
}
}
// Performs Hoare partition algorithm for quicksort
private static int partition(int[] ar, int lo, int hi) {
int pivot = ar[lo];
int i = lo - 1, j = hi + 1;
while (true) {
do {
i++;
} while (ar[i] < pivot);
do {
j--;
} while (ar[j] > pivot);
if (i < j) swap(ar, i, j);
else return j;
}
}
// Swap two elements
private static void swap(int[] ar, int i, int j) {
int tmp = ar[i];
ar[i] = ar[j];
ar[j] = tmp;
}
public static void main(String[] args) {
InplaceSort sorter = new QuickSort();
int[] array = {10, 4, 6, 4, 8, -13, 2, 3};
sorter.sort(array);
// Prints:
// [-13, 2, 3, 4, 4, 6, 8, 10]
System.out.println(java.util.Arrays.toString(array));
}
}