/*==============================================================
  ArrayQueue implement Queue interface using a circular array
  ============================================================== */

public class ArrayQueue  implements Queue
{
   /* ==========================================
      Node "inner class"
      ========================================== */
   public class Node
   {
      double value;
      Node   next;

      public Node( double x )
      {
         value = x;
         next  = null;   
      }

      public String toString()
      {
         return "" + value;
      }
   }

   public double[] buf;          // Circular buffer
   public int      read, write;  // read and write pointers

   // Constructor
   public ArrayQueue(int size)
   {
      buf = new double[size];    // Create array for circular buffer

      read = 0;                  // Initialized read & write pointers
      write = 0;
   }

   /* ====================================================
       enqueue(x ): 
      ==================================================== */
   public void enqueue( double x )   throws Exception
   {
      if ( read == ( write + 1 ) % (buf.length) )
      {
	 throw new Exception("Queue is full");
      }

      buf[write] = x;                 // Store x in buf at write pointer    
      write = (write+1)%(buf.length); // Advance the write pointer
   }

   /* ====================================================
       dequeue(): 
      ==================================================== */
   public double dequeue( ) throws Exception
   {
      double r;   // Variable used to save the return value     

      if ( read == write )
      {
	 throw new Exception("Queue is empty");
      }

      r = buf[read];                 // Save return value
      read = (read+1)%(buf.length);  // Advance the read pointer

      return r;
   }

   /* ====================================================
      Convert all elems in the list into a string:

       Format:"v1,v2,v3,..."
      ==================================================== */
   public String toString()
   {
      String out;
      int i;

      out = "[";

      for ( i = read; ((i)%buf.length) != write; i++ )
      {
         out += buf[i];       // Concat next list element  

         if ( ((i+1)%buf.length) != write )
            out += " , ";     // Not last elem: add a ","
      }

      out += "]";
      return out;
   }
}