QuickSort.java

public static void quickSort(int array[]) {
  quickSort(array, 0, array.length - 1);
}

public static void quickSort(int array[], int start, int end) {
  int i = start;
  int k = end;

  if (end - start >= 1) {
    int pivot = array[start];
    while (k > i) {
      while (array[i] <= pivot && i <= end && k > i) {
        i++;
      }
      while (array[k] > pivot && k >= start && k >= i) {
        k--;
      }
      if (k > i) {
        swap(array, i, k);
      }
    }
    swap(array, start, k);

    quickSort(array, start, k - 1);
    quickSort(array, k + 1, end);
  } else {
    return;
  }
}

public static void swap(int array[], int index1, int index2) {
  int temp = array[index1];
  array[index1] = array[index2];
  array[index2] = temp;
}