// This program uses code from "Algorithms in C, Third Edition,"
//               by Robert Sedgewick, Addison-Wesley, 1998.


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

typedef int Item;
#define key(A) (A)
#define less(A, B) (key(A) < key(B))
#define exch(A, B) { Item t = A; A = B; B = t; } 
#define compexch(A, B) if (less(B, A)) exch(A, B)

int partition(Item a[], int l, int r)
{ 
  int i = l-1, j = r; 
  Item v = a[r];
  for (;;)
  { 
    while (less(a[++i], v)) ;
    while (less(v, a[--j])) if (j == l) break;
    if (i >= j) break;
    exch(a[i], a[j]);
  }
  exch(a[i], a[r]);
  return i;
}


void quicksort_helper(Item a[], int l, int r)
{ 
  int i;
  if (r <= l) return;
  i = partition(a, l, r);
  quicksort_helper(a, l, i-1);
  quicksort_helper(a, i+1, r);
}

void quicksort(Item a[], int length)
{
  quicksort_helper(a, 0, length-1);
}


void print_array(int * a, int length)
{
  int counter;
  for (counter = 0; counter < length; counter++)
  {
    printf ("%2d: %d\n", counter, a[counter]);
  }
  printf("\n");
}

int main()
{
//  int a[] = {17, 90, 70, 30, 60, 40, 45, 80, 10, 35}; 
  int a[] = {10, 17, 30, 35, 60, 40, 45, 80, 90, 70}; 
  print_array(a, 10);

  partition(a, 4, 9); 
//  partition(a, 2, 6); 
//  quicksort(a, 10); 

  print_array(a, 10);

  return 0;
}