Heapmax.java

 import java.util.*;
 
 class Maxheap{
     private int arr[];
     private int size;
     private int max;

     public Maxheap(int max){
          arr=new int[max];
          this.max=max;
          size=0;

     }
     private int parent(int i){
          return i/2;
     }
     private int left(int i){
          return 2*i;
     }
     private int right(int i){
          return (2*i)+1;
     }

     public boolean insert(int val){
          if(size==max-1)
          return false;
          size++;
          arr[size]=val;
          int i=size;
          while(arr[parent(i)]<arr[i]&& i!=1){
               int temp=arr[i];
               arr[i]=arr[parent(i)];
               arr[parent(i)]=temp;
               i=parent(i);
          }
          return true;
     }
     public void display(){
          for(int i=1;i<=size;i++){
               System.out.println(arr[i]);
          }
     }

     private void Maxheapify(int i){
          if(size!=0){
               int c1,c2;
               c1=left(1);
               c2=right(i);
               if(c1<size&&c2<size){
                    if(arr[i]<arr[c1]||arr[i]<arr[c2]){
                         if(arr[c1]>arr[c2]){
                              int temp=arr[i];
                              arr[i]=arr[c1];
                              arr[c1]=arr[i];
                              Maxheapify(c1);
                         }
                         else{
                              int temp=arr[i];
                              arr[i]=arr[c2];
                              arr[c2]=arr[i];
                              Maxheapify(c2);
                         }
                    }
               }
          }

     }
     public int extractMax(){
          if(size==0)
          return -1;
          int val=arr[1];
          arr[1]=arr[size];
          size--;
          Maxheapify(1);
          return val;
     }



}


public class Heapmax{
     public static void main(String[]args){
          int max;
          Scanner s= new Scanner(System.in);
          System.out.println("enetr max :");
          max=s.nextInt();
          Maxheap h= new Maxheap(max);
          boolean temp=true;
          int choice;
          while(temp){
               System.out.println("1 to insert");
               System.out.println("2 to pop");
               System.out.println("3 to display");
               System.out.println("4 to exit");
               choice=s.nextInt();
               switch(choice){
                    case 1:
                    choice=s.nextInt();
                    if(h.insert(choice)){
                         h.display();
                    }
                    else{
                         System.out.println("Cannot do this!");
                    }
                    break;
                    case 2:
                    choice=h.extractMax();
                    if(choice==-1)
                    System.out.println("Cannot do this!");
                    else
                    System.out.println(choice);
                    break;
                    case 3:
                    h.display();
                    break;
                    case 4:
                    temp=false;
                    break;
                    default:
                    System.out.println("Enter the correct choice!");


               }
          }
     }
}