programming-examples/c/Search_Sorting/C Program to demonstrate non recursive quick sort.C

/* Program to demonstrate non recursive quick sort */

#include  <stdio.h>
#include  <conio.h>
#define  STACKSIZE  50

struct  bounds
{
    int  lb, ub ;
} ;

struct  stack
{
    int  top ;
    struct  bounds  items[STACKSIZE] ;
} ;

void  quick(int  x[ ], int  n) ;
int  partition(int  x[ ], int  lb, int  ub) ;
void  show(int  x[ ], int  lb, int  ub) ;

void  push(struct  stack  *ps, struct  bounds  x) ;
struct  bounds  pop(struct  stack  *ps) ;
int  empty(struct  stack  *ps) ;

void  main()
{
    int  i, n, x[20] ;
    clrscr() ;
    printf("Enter the number of elements: ") ;
    scanf("%d",&n) ;
    printf("Enter the elements:\n") ;
    for(i=0 ; i<n ; i++)
        scanf("%d",&x[i]) ;
    quick(x,n) ;
    printf("Sorted array is as shown:\n") ;
    for(i=0 ; i<n ; i++)
        printf("%d ",x[i]) ;
    getch() ;
}

void  quick(int  x[ ], int  n)
{
    int  temp, j ;
    struct  bounds  b ;
    /*Initializing the stack to be empty*/
    struct  stack  s ;
    s.top=-1 ;
    b.lb=0 ;
    b.ub=n-1 ;
    push(&s,b) ;
    /*Repeat as long as there are any unsorted sub-arrays*/
    while(!empty(&s))
        {
            b=pop(&s) ;
            while(b.ub>b.lb)
                {
                    j=partition(x,b.lb,b.ub) ;
                    if(j-b.lb>b.ub-j)
                        {
                            /* stack the lower sub-array */
                            temp=b.ub;
                            b.ub=j-1;
                            push(&s,b);
                            /* Process the upper sub-array */
                            b.lb=j+1;
                            b.ub=temp;
                        }
                    else
                        {
                            /* stack the upper sub-array */
                            temp=b.lb;
                            b.lb=j+1;
                            push(&s,b);
                            /* Process the lower sub-array */
                            b.ub=j-1;
                            b.lb=temp;
                        }
                }
        }
}

int  partition(int  x[ ], int  lb, int  ub)
{
    int  a, down, up, temp ;
    a=x[lb] ;
    up=ub ;
    down=lb ;
    while(down<up)
        {
            while(x[down]<=a&&down<ub)
                down++ ;
            while(x[up]>a)
                up-- ;
            if(down<up)
                {
                    temp=x[down];
                    x[down]=x[up];
                    x[up]=temp;
                }
        }
    x[lb]=x[up] ;
    x[up]=a ;
    show(x,lb, ub) ;
    return up ;
}

void  show(int  x[ ], int  lb, int  ub)
{
    int  i ;
    for(i=lb ; i<=ub ; i++)
        printf("%d ", x[i]) ;
    printf("\n\n") ;
}

void  push(struct  stack  *ps, struct  bounds  x)
{
    if(ps->top==STACKSIZE-1)
        {
            printf("Stack Overflow. Cannot push. \n") ;
            getch() ;
            exit(1) ;
        }
    ps->items[++(ps->top)]=x ;
}

struct  bounds  pop(struct  stack  *ps)
{
    if(empty(ps))
        {
            printf("Stack Underflow. Cannot pop. \n") ;
            getch() ;
            exit(1) ;
        }
    return(ps->items[(ps->top)--]) ;
}

int  empty(struct  stack  *ps)
{
    if(ps->top==-1)
        return  1 ;
    else
        return  0 ;
}


/* The method show() is optional. It is written to show output of each pass. It may not be written in theory exam. It is required only in practical exams */