Question

In java please:

Write a method that accepts as a parameter a queue of integers that are already sorted by absolute value, and modifies it so that the integers are sorted normally. Only use a single stack as auxiliary storage. For example, if a queue variable named q stores the following elements:

front {1, -2, 4, 5, -7, -9, -12, 28, -34} back
Then the call of reorder(q); should modify it to store the following values:

front {-34, -12, -9, -7, -2, 1, 4, 5, 28} back

Answer 1

Solution :

import java.util.*;
class Solution
{
   // This method accepts a parameter a queue of integers that are already sorted by absolute value, and modifies it so that the integers are sorted normally.
   public void reorder(Queue<Integer> q)
   {
       // creating a single stack of Integer as auxiliary storage
       Stack<Integer> s = new Stack<Integer>();
      
       // getting the size of the given queue
       int size = q.size();
      
       // this is a temporary variable which will store the count of positive values of the given queue
       int count = 0;          
      
       // iterating for all the values of the given queue
       for(int i = 0; i < size; i++)
       {
           int front_val = q.remove();               // getting the front value of the given queue and removing it
          
           // if the front value of the given queue is negative, then push it to the stack
           if(front_val < 0)           
               s.push(front_val);
          
           // else adding the front value to the back of the queue again
           else if( front_val >= 0 )
           {
               q.add(front_val);
               count++;               // also incrementing the count of positive values of the given queue
           }
       }
      
       // adding all the elements of the stack one by one to the back of the given queue
       while(!s.isEmpty())
           q.add(s.pop());
      
       // now adding all the positive values of the queue to the back of the queue again
       for(int i = 0; i < count; i++)
           q.add(q.remove());
      
       // printing all the values of the queue in normally sorted order
       System.out.print("\nSorted Elements are : " + q );
      
       // printing a new line
       System.out.println();
   }
  
   // this part of the code is only for checking the correctness of the output
   public static void main(String args[])
   {
       // creating a queue of Integer
       Queue<Integer> q = new LinkedList<>();
      
       // adding all the given elements to the queue ( only for checking the correctness of the code )
       q.add(1);
       q.add(-2);
       q.add(4);
       q.add(5);
       q.add(-7);
       q.add(-9);
       q.add(-12);
       q.add(28);
       q.add(-34);
      
       // creating an object for calling reorder() to get the expected output
       Solution obj = new Solution();
      
       // calling reorder() to get the expected output as in the given question and passing q to it
       obj.reorder(q);
   }
}

Output :