As the name implies, it is quick, and it is the algorithm
generally preferred for sorting.The steps involved are
Pick an element, say P (the pivot) .Re-arrange the elements
into 3 sub-blocks,
1. those less than or equal to ( ≤ ) P (the left- block S1 )
2. P (the only element in the middle -block)
3. those greater than or equal to ( ≥ ) P (the right-
block S2 )
Repeat the process recursively for the left- and right- sub-blocks.
Return {quicksort(S1 ), P , quicksort( S2 )}.
(That is the results of quicksort(S1), followed by P,
followed by the results of quicksort(S2))
Quick Sort Program
#include<conio.h>
void main()
{
int i,k,l=1,u,n,a[20];
void qsort(int a[],int l,int u);
clrscr();
printf("Enter number of elements");
scanf("%d",&n);
printf(" Enter elements");
for (i=1; i<=n;i++)
scanf("%d",&a[i]);
u=n;
qsort(a,l,u);
for(i=1;i<=n;i++)
printf("%5d",a[i]);
getch();
}
void qsort(int a[],int l,int u)
{
int i,j,t, flag=1,key;
i=l;
j=u+1;
if(l<u)
{
key=a[i]; // pivot point
while( flag==1) // spitting the block pf datadata into 2 . A sublock containg data less then key and the
//other greater than key
{
i++;
while (a[i]<key)
i++;
j--;
while (a[j]>key)
j--;
if(i<j) // swap the key to make it the center of the 2 sub block
{
t=a[i];
a[i]=a[j];
a[j]=t;
}
else
flag=0;
}
t=a[l];
a[l]=a[j];
a[j]=t;
qsort(a,l,j-1); //recursively calling qsort to sort lower sub block
qsort( a,j+1, u); //recursively calling qsort to sort upper sub block
}
}
