/*
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 * This program demonstrates the use of the quick sort algorithm.  For
 * more information about this and other sorting algorithms, see
 * http://linux.wku.edu/~lamonml/kb.html
 *
 */
 
/*******
 * Jim M says :
 * This is from from http://linux.wku.edu/~lamonml/algor/sort/quick.html on 2/14/2007 .
 * Running it looks like this.
 *
 *     $ make quick
 *     gcc -march=athlon64 -O2    quick.c   -o quick
 *     $ ./quick
 *     Done with sort.
 *     23800775
 *     43276221
 *     ...
 *     2005741260
 *     2009715262
 *     2029398822
 *     2070874944
 *     2073793258
 * 
 ***********/

#include <stdlib.h>
#include <stdio.h>

#define NUM_ITEMS 100

void quickSort(int numbers[], int array_size);
void q_sort(int numbers[], int left, int right);

int numbers[NUM_ITEMS];

int main(){
  int i;

  //seed random number generator
  srand(getpid());

  //fill array with random integers
  for (i = 0; i < NUM_ITEMS; i++){
    numbers[i] = rand();
  }

  //perform quick sort on array
  quickSort(numbers, NUM_ITEMS);

  printf("Done with sort.\n");
  for (i = 0; i < NUM_ITEMS; i++){
    printf("%i\n", numbers[i]);
  }
}
 
void quickSort(int numbers[], int array_size){
  q_sort(numbers, 0, array_size - 1);
}

void q_sort(int numbers[], int left, int right){
  int pivot, l_hold, r_hold;

  l_hold = left;
  r_hold = right;
  pivot = numbers[left];
  while (left < right) {
    while ((numbers[right] >= pivot) && (left < right)){
      right--;
    }
    if (left != right) {
      numbers[left] = numbers[right];
      left++;
    }
    while ((numbers[left] <= pivot) && (left < right)){
      left++;
    }
    if (left != right) {
      numbers[right] = numbers[left];
      right--;
    }
  }
  numbers[left] = pivot;
  pivot = left;
  left = l_hold;
  right = r_hold;
  if (left < pivot){
    q_sort(numbers, left, pivot-1);
  }
  if (right > pivot){
    q_sort(numbers, pivot+1, right);
  }
}