HEAP SORT ALGORITHM IN JAVA.

/*
TOPIC: HEAP SORT ALGORITHM.
DATE:3/10/2012
*/

import java.io.*;
class Sequence
{
int size;
int i;
int a[]=new int[25];
BufferedReader br;
Sequence()
{
br = new BufferedReader ( new InputStreamReader(System.in));
}
void create()throws IOException
{
System.out.println("enter size of array: ");
size=Integer.parseInt(br.readLine());
a=new int[size];
insert();
}
void insert()throws IOException
{
System.out.println("INSERT THE ELEMENTS INTO THE ARRAY");
for(int i=0;i<size;i++)
a[i]=Integer.parseInt(br.readLine());
}

void display()
{
for(int i=0;i<a.length;i++)
System.out.print(a[i]+" ");
System.out.println();
}
void HeapSort()
{
int n=size;
int i,elt,s,f,ivalue,pass=1;
    for(i=1;i<n;i++)
    {
elt=a[i];
s=i;
f=(s-1)/2;
while((s>0)&&(a[f]<elt))
{
   a[s]=a[f];
   s=f;
   f=(s-1)/2;
}
a[s]=elt;
    }
    for(i=n-1;i>0;i--)
    {
ivalue=a[i];
a[i]=a[0];
f=0;
if(i==1)
s=-1;
else
s=1;
if((i>2)&&(a[2]>a[1]))
s=2;
while((s>=0)&&(ivalue<a[s]))
{
   a[f]=a[s];
   f=s;
   s=2*f+1;
   if((s+1<=i-1)&&(a[s]<a[s+1]))
       s=s+1;
   if(s>(i-1))
s=-1;
}
       a[f]=ivalue;
System.out.println();
    }

}
}  
class HeapSort
{
public static void main(String args[])throws IOException
{
      Sequence s=new Sequence();
s.create();
System.out.println("BEFORE SORTING:");
s.display();
    s.HeapSort();
    System.out.println("AFTER SORTING:");
 
s.display();
}

}
/*
OUTPUT:
enter size of array:
8
INSERT THE ELEMENTS INTO THE ARRAY
25
4
65
9
555
1
23
12
BEFORE SORTING:
25              4               65              9               555            23               12
AFTER SORTING:
1               4               9               12              23             25               65              555

*/