a_134_QueueB.java

public class a_134_QueueB {

    // static class Queue {
    //     static int arr[]  ;
    //     static int size  ;
    //     static int rear  ;

    //     Queue (int n){
    //         arr = new int[n] ;
    //         size = n ;
    //         rear = -1 ;
    //     }

    //    // methods 
    //     public static boolean isEmpty(){
    //        return rear == -1 ;
    //    } 

    //    // add 
    //    public static void add(int data) {
    //     if( rear == size-1 ) {
    //         System.out.println("Queue is full");
    //       return ;
    //     }

    //     rear = rear + 1 ;
    //     arr[rear] = data ;

    //    }

    //    // Remove 
    //    public static int remove(){
    //     if(isEmpty()){
    //         System.out.println("Queue is Empty");
    //         return -1; 
    //     }

    //     int front = arr[0] ;
    //     for(int i=0; i<rear; i++ ){
    //         arr[i] = arr[i+1] ;
    //     }
    //       rear = rear - 1 ;
    //     return front ;
    //    }

    //    // peek
    //    public static int peek(){
    //     if(isEmpty()){
    //         System.out.println("Queue is Empty");
    //         return -1; 
    //     }

    //     return arr[0] ;
    //    }

        
    // }


    // Circular Queue using Arrays
    static class Queue {
        static int arr[]  ;
        static int size  ;
        static int rear  ;
        static int front ;

        Queue (int n){
            arr = new int[n] ;
            size = n ;
            rear = -1 ;
            front = -1 ;
        }

       // methods 
        public static boolean isEmpty(){
           return rear == -1 && front == -1 ;
       } 

       public static boolean isFull() {
         return (rear + 1) % size == front  ;
       }

       // add 
       public static void add(int data) {
        if( isFull() ) {
            System.out.println("Queue is full");
          return ;
        }

        // add first element 
        if(front == -1) {
           front = 0 ; 
        }

        rear = (rear + 1) % size ;
        arr[rear] = data ;

       }

       // Remove 
       public static int remove(){
        if(isEmpty()){
            System.out.println("Queue is Empty");
            return -1; 
        }

        int result = arr[front] ;
        // last element delete 
        if(front == rear ){
            front = rear = -1 ;
        }
        else{
            front = (front+1) % size ;
        }

        return result ;
       }

       // peek
       public static int peek(){
        if(isEmpty()){
            System.out.println("Queue is Empty");
            return -1; 
        }

        return arr[front] ;
       }

    }

    public static void main(String[] args) {
        Queue q = new Queue(3)  ;
     
        q.add(1); 
        q.add(2); 
        q.add(3);

        System.out.println(q.remove());
        q.add(4);
        System.out.println(q.remove());
        q.add(5);
        

        while(!q.isEmpty()){
            System.out.println(q.peek());
            q.remove() ;
        }
        
         
    }

}