Question

Write a method called reverseFirstK that accepts an integer k and a queue of integers as parameters and reverses the order of the first k elements of the queue, leaving the other elements in the same relative order. For example, if a queue named q stores [10, 20 30, 40, 50, 60, 70, 80, 90], the call of reverseFirstK (4, q):should change the queue to store [40, 30 20, 10, 50, 60, 70, 80, 90]. If k is 0 or negative, no change should be made. If the queue does not contain at least k elements, your method should throw an IllegalArgumentException. Use one queue or stack (but not both) as auxiliary storage.

Answer 1

import java.util.Queue;

public class ReverseKelements {

   static void QueueUtil(Queue<Integer> s, int item) {

  

       s.add(item);

      

          

   }

   static void UtilQueue(Queue<Integer> q, int temp) {

       if (q.isEmpty()) {

          

           return;

       }

       int t = q.poll();

       UtilQueue(q, t);

      

       QueueUtil(q, t);

   }

   public static void reverseFirstK(Queue<Integer> queue, int k) {

       if(k<=0 )

           return;

      

       if(k>queue.size())

           throw new IllegalArgumentException();

      

       Queue<Integer> pq = new java.util.LinkedList<Integer>();

       for(int i=0;i<k;++i){

           pq.add(queue.poll());

       }

      

       UtilQueue(queue, queue.peek());

       while(!pq.isEmpty()){

           queue.add(pq.poll());

       }

      

       UtilQueue(queue, queue.peek());

      

   }

   public static void main(String[] args) {

       // TODO Auto-generated method stub

      

      

      

       Queue<Integer> queue = new java.util.LinkedList<Integer>();

       queue.add(10);

       queue.add(20);

       queue.add(30);

       queue.add(40);

       queue.add(50);

       queue.add(60);

       queue.add(70);

       queue.add(80);

       queue.add(90);

      

       System.out.println("Queue Before: ");

       System.out.println(queue.toString());

       reverseFirstK(queue,4);

       System.out.println("Queue After Reverse: ");

       System.out.println(queue.toString());

      

   }

}
==================================================
See Output


D D Stack-Java for(int 1k;++1)1 Stacklnterface M stack-Java d!!胤Problems Search 리 Console ×「Progress . 32 <terminated> ReverseKelements [Java Application] /Library/Interne Queue Before: [10, 20, 30, 40, 50, 60, 70, 80, 90] Queue After Reverse: C40, 30, 20, 10, 50, 60, 70, 80, 90] pq.add(queue.pollo); 35 36 37 38 39 40 41 42 UtilQueue(queue, queue.peek)); while(!pq.isEmptyO)[ queue.add(pq.pollo); UtilQueue(queue, queue.peekO); public static void main(String[] args) 7TODO Auto-generated method stub 47 48 49 50 51 52 53 54 Queue<Integer> queuenew java.util queue.add(10); queue.add(20); queue.add(30); queue.add(40); queue.add(50); queue.add(60); queue.add(70); queue.add(80); queue.add(90); 56 57 58 59 60 61 62 63 64 65 System.out.println("Queue Before:" System.out.println(queue.toString)) reverseFirstK(queue,4); System.out.println("Queue After Reve System.out.println(queue.toStringO) 68 69 70 71 72

Thanks