Mega Code Archive
Handles QuickSort and all of its methods
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//package sortcomparisons;
import java.util.Random;
/**
* Handles QuickSort and all of its methods.
*
* @author Alex Laird
* @version 1.0
*/
public class QuickSort
{
// object pointer delcarations
private static final Random random = new Random();
/**
* Swaps the two indeces in the array given.
*
* @param array The array to perform the swap on.
* @param first The first index to swap.
* @param second The second index to swap.
*/
private void swap(int[] array, int first, int second)
{
// swap array[i] and array[j]
int temp = array[first];
array[first] = array[second];
array[second] = temp;
}
/**
* Finds the most logical point to split the array in two parts and uses
* that point as the partition. Uses a for loop to evaluate the partition.
*
* @param array The array to be sorted.
* @param low The lowest index.
* @param high The highest index.
* @return The index of the partitioning point.
*/
private int partitionUsingFor(int[] array, int low, int high)
{
// get the value of the pivot element
int pivot = array[high];
// the low pointer
int i = low - 1;
for(int j = low; j < high; ++j)
{
// if the value at the current index in the array is smaller than the pivot, swap them
if(array[j] <= pivot)
{
i = ++i;
// swap array[i] and array[j]
swap(array, i, j);
}
}
// increment the low pointer
++i;
// swap array[i] and array[high]
swap(array, i, high);
return i;
}
/**
* Finds the most logical point to split the array in two parts and uses
* that point as the partition. Uses a while loop to evaluate the partition.
*
* @param array The array to be sorted.
* @param low The lowest index.
* @param high The highest index.
* @return The index of the partitioning point.
*/
private int partitionUsingWhile(int[] array, int low, int high)
{
int pivot = array[low];
int left = low;
int right = high;
while(left < right)
{
// increment the low pointer until you meet the pivot
while(left <= right && array[left] <= pivot)
{
++left;
}
// decrement the high pointer until you meet the pivot
while(left <= right && array[right] > pivot)
{
--right;
}
// if the pointers have crossed, swap the items
if(left < right)
{
// swap array[left] with array[right]
swap(array, left, right);
}
}
array[low] = array[right];
array[right] = pivot;
return right;
}
/**
* Generates the random partition location and calls the partition method.
* Uses a for loop to evaluate the partition.
*
* @param array The array to be sorted.
* @param low The lowest index.
* @param high The highest index.
* @return The index of the randomly generated partition.
*/
private int randomizedPartitionUsingFor(int[] array, int low, int high)
{
// some random int between low and high
int i = random.nextInt(high - low + 1) + low;
// swap array[high] and array[i]
swap(array, high, i);
return partitionUsingFor(array, low, high);
}
/**
* Generates the random partition location and calls the partition method.
* Uses a while loop to evaluate the partition.
*
* @param array The array to be sorted.
* @param low The lowest index.
* @param high The highest index.
* @return The index of the randomly generated partition.
*/
private int randomizedPartitionUsingWhile(int[] array, int low, int high)
{
// some random int between low and high
int i = random.nextInt(high - low + 1) + low;
// swap array[high] and array[i]
swap(array, high, i);
return partitionUsingWhile(array, low, high);
}
/**
* Performs a recursive QuickSort algorithm on an array from low to high, but
* does so by selecting randomized indeces for the partitions. Uses a for
* loop to evaluate the partition.
*
* @param array The array to be sorted.
* @param low The lowest index.
* @param high The highest index.
*/
public void sortRandomizedPartitionUsingFor(int[] array, int low, int high)
{
if(low < high)
{
// randomly locate a partition point
int mid = randomizedPartitionUsingFor(array, low, high);
// recursively sort the lower portion
sortRandomizedPartitionUsingFor(array, low, mid - 1);
// recursively sort the upper portion
sortRandomizedPartitionUsingFor(array, mid + 1, high);
}
}
/**
* Performs a recursive QuickSort algorithm on an array from low to high, but
* does so by selecting randomized indeces for the partitions. Uses a while
* loop to evaluate the partition.
*
* @param array The array to be sorted.
* @param low The lowest index.
* @param high The highest index.
*/
public void sortRandomizedPartitionUsingWhile(int[] array, int low, int high)
{
if(low < high)
{
// randomly locate a partition point
int mid = randomizedPartitionUsingWhile(array, low, high);
// recursively sort the lower portion
sortRandomizedPartitionUsingWhile(array, low, mid - 1);
// recursively sort the upper portion
sortRandomizedPartitionUsingWhile(array, mid + 1, high);
}
}
/**
* Performs a standard recursive QuickSort algorithm on an array from high
* to low. Uses a for loop to evaluate the partition.
*
* @param array The array to be sorted.
* @param low The lowest index.
* @param high The highest index.
*/
public void sortUsingFor(int[] array, int low, int high)
{
if(low < high)
{
// locate the most precise partition point
int mid = partitionUsingFor(array, low, high);
// recursively sort the lower half
sortUsingFor(array, low, mid - 1);
// recursively sort the upper half
sortUsingFor(array, mid + 1, high);
}
}
/**
* Performs a standard recursive QuickSort algorithm on an array from high
* to low. Uses a while loop to evaluate the partition.
*
* @param array The array to be sorted.
* @param low The lowest index.
* @param high The highest index.
*/
public void sortUsingWhile(int[] array, int low, int high)
{
if(low < high)
{
// locate the most precise partition point
int mid = partitionUsingWhile(array, low, high);
// recursively sort the lower half
sortUsingWhile(array, low, mid - 1);
// recursively sort the upper half
sortUsingWhile(array, mid + 1, high);
}
}
}
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