Queue

Description

• A QUEUE is an ADT (abstract data type) in FIFO order (first in, first out).
• It has 2 main operations: (1) ENQUEUE or adding on the tail/back, and (2) DEQUEUE or removing on the head/front.
• It is a protected SINGLY LINKED LIST where enqueue and dequeue are only allowed on the top front or last element in the queue.
• You may also PEEK to show the last element added.
• Implementation can either be in ARRAY or LINKED LIST.
• It's algorithmic complexity is CONSTANT or O(1) for both ends (enqueue, dequeue).

To Do:

• Implement a QUEUE using ARRAY that can hold a maximum of 10 integers.
• Create operations ENQUEUE, DEQUEUE, and PEEK.
• Allow ENQUEUE only if the queue is not yet full.
• Allow DEQUEUE only if the queue is not yet empty.
• Upon DEQUEUE, shift the element's position accordingly.
• Allow PEEK to see the topmost topmost element.
• Show the updated ARRAY QUEUE for every successful ENQUEUE and DEQUEUE.

Pseudocode:

START PROGRAM

 SET capacity, head, tail, items, queue[]
 SET tail = items-1
     
 PROCEDURE show
  FOR EACH value IN queue.capacity
   PRINT queue[adjust(head.next)]

 PROCEDURE isEmpty
  IF items == 0
   PRINT queue is empty
   return TRUE

 PROCEDURE isFull
 IF items == capacity
   PRINT queue is full
   return TRUE

 PROCEDURE enqueue(value)
  IF isFull
   PRINT add failed.
  ELSE        
    PRINT trying to enqueue on queue[tail]
    queue[adjust head items] = value
    items++
    PRINT element was successfully added

 PROCEDURE dequeue
  IF isEmpty
   PRINT remove failed.
  ELSE
   PRINT trying to dequeue head
   int temp = storage[head];
   queue[head] = 0
   head.next = head
   head--
   PRINT queue[head] was successfully removed
  
 PROCEDURE peekHead
  IF isEmpty
   PRINT 0
  ELSE 
   PRINT head
 
 PROCEDURE peekTail
  IF isEmpty
   PRINT 0
  ELSE 
   PRINT tail

 PROCEDURE main
 // show that queue is empty
 // enqueue 10 integers until queue is full
 // show updated queue
 // try to enqueue again, return error message
 // dequeue last element
 // peek last element
 // dequeue all elements until queue is empty
 // show updated queue
 // try to dequeue again, return error message

END PROGRAM