quicksort.java

/**
 * Recursive quicksort method. Pivot is calculated at 1/2 the difference
 * between supplied bounds.
 * 
 * @param lowerBound
 *            the lower bound of indexed inputs - e.g., usually 0
 * @param upperBound
 *            the upper bound of indexed inputs - e.g., usually array.length
 * @param array
 *            the array to sort
 */
private static void quickSort(int lowerBound, int upperBound, int[] array) {

	int i = lowerBound;
	int j = upperBound;
	int pivot = array[lowerBound + (upperBound - lowerBound) / 2];

	while (i <= j) {

		while (array[i] < pivot) {
			i++;
		}

		while (array[j] > pivot) {
			j--;
		}

		if (i <= j) {

			int temp = array[i];

			array[i] = array[j];
			array[j] = temp;

			i++;
			j--;
		}
	}

	if (lowerBound < j) {
		quickSort(lowerBound, j, array);
	}

	if (i < upperBound) {
		quickSort(i, upperBound, array);
	}
}