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package sorting.algorithms;

/**

* Choose a pivot value, Partition and Sort both parts. Recursive operation.

* O(n log n)

* <p/>

* User: rpanjrath

* Date: 8/20/13

* Time: 2:55 PM

*/

public class QuickSort {

private int[] inputArray;

private int length;

public int[] sort(int[] values) {

// Check for empty or null array

if (values == null || values.length == 0) {

return values;

}

this.inputArray = values;

length = values.length;

quicksort(0, length - 1);

return values;

}

private void quicksort(int low, int high) {

int i = low, j = high;

// Get the pivot element from the middle of the list

int pivot = inputArray[low + (high - low) / 2];

// Divide into two lists

while (i <= j) {

// If the current value from the left list is smaller then the pivot

// element then get the next element from the left list.

// If current value is greater than pivot value then stop!

while (inputArray[i] < pivot) {

i++;

}

// If the current value from the right list is larger then the pivot

// element then get the next element (continue) from the right list.

// If current value is less than pivot value then stop!

while (inputArray[j] > pivot) {

j--;

}

// If we have found a values in the left list which is larger then

// the pivot element and if we have found a value in the right list

// which is smaller then the pivot element then we exchange the

// values.

// As we are done we can increase i and j

if (i <= j) {

exchange(i, j);

i++;

j--;

}

}

// Recursion

if (low < j)

quicksort(low, j);

if (i < high)

quicksort(i, high);

}

private void exchange(int i, int j) {

int temp = inputArray[i];

inputArray[i] = inputArray[j];

inputArray[j] = temp;

}

}