Top 9 Differences between Stack And Queue

Top 9 Differences between Stack And Queue

Hey learners! What’s going on? How’s your coding journey going on? Are you ready to learn another new topic in this programming journey of yours? I hope so.

Before we start today’s topic, I have a small question for you. Do you know how to check parenthesis matching in an expression? Did you ever convert one form of expression to another form?

If you are a developer, did you ever serve requests on a single shared resource? All such things can be done using Stack and Queue in data structures. So, in this article, today you are going to know about a Stack and a Queue, how to use them, and also the major differences between them. So, I suggest you read this article till the end.

What is a Stack?

A stack in a programming language can be defined as an array or list structure of function calls and parameters. A stack is generally used in modern computer programming and CPU architecture. To understand a stack, there are many real-life examples. For example, we can simply assume that a stack is similar to a stack of plates at a buffet restaurant or cafeteria. You can add or remove the elements in a stack from the top of the stack, in a “last in first out” order or it is also called the LIFO order.

There are two major operations in a Stack that are used for adding and removing the elements in the stack. These two operations are known as PUSH and POP operations. It is very important to know how to implement these add and remove functions in a stack. Usually, you will have to declare an empty list and use the append() and pop() methods to add and remove the data elements in a Stack.

Let us look at an example to know how to perform POP and PUSH operations in a Stack. So, consider the following examples.

Example-1:

class StackExample:

   def __init__(self):

      self.stack = []

   def add(self, dataval):

# Here, you need to use the list append method to add an element

      if dataval not in self.stack:

         self.stack.append(dataval)

         return True

      else:

         return False

# Here you will use peek so that you can be able to look at the top of the stack

   def peek(self):    

               return self.stack[-1]

AStack = StackExample()

AStack.add(“Monday”)

AStack.add(“Tuesday”)

AStack.peek()

print(AStack.peek())

AStack.add(“Wednesday”)

AStack.add(“Thusday”)

print(AStack.peek())

After executing the above program, you will get the following result as output.

Output:

Tuesday

Thursday

The above example program explains to you about the PUSH() operation in a Stack. Now, you are going to know about a POP() operation in a Stack using the following example.

Consider the following example:

Example-2:

class StackExample:

   def __init__(self):

      self.stack = []

   def add(self, datavalue):

# You can use the list append method to add any element

      if datavalue not in self.stack:

         self.stack.append(datavalue)

         return True

      else:

         return False

# Here, you need to use the list pop method to remove an element

   def remove(self):

      if len(self.stack) <= 0:

         return (“There is no element found in the Stack”)

      else:

         return self.stack.pop()

AStack = StackExample ()

AStack.add(“Monday”)

AStack.add(“Tuesday”)

AStack.add(“Wednesday”)

AStack.add(“Thusday”)

print(AStack.remove())

print(AStack.remove())

After executing the above program, you will get the following result as output.

Output:

Thursday

Wednesday

The above example program explains to you about the POP() operation in a Stack. Actually, you know that it is possible to remove only the top most data element from the stack. But in the above program, we have implemented a python program that removes only the top most element using the remove function which returns the top most element. You need to calculate the size of the stack first and then use the in-built pop() method to check the top element and hence you can find out the top most element.

So, this is the basic information about a Stack. Now, you are going to know some basic things about a Queue in data structures.

What is a Queue?

A queue is defined as a collection of operations or structures that should be maintained in a sequence. You can modify a queue by adding these operations or structures at one end of the sequence and removing them from the other end of the sequence. This is how we define a queue generally in computer science programming.

Unlike a stack, A queue is a first-in-first-out (FIFO) abstract data type that can be heavily used in computing. To explain it clearly, consider the ticket queue outside a cinema hall as an example. In this situation or example, the first person who enters the queue will get the person the ticket first, and so on. Queue follows the similar rule shown in the above example. It means that the item that goes in first is the item that comes out first.

In programming, a queue is used in many cases such as:

  • You can be able to manage requests on a single shared resource

Example:

CPU scheduling and disk scheduling.

  • You can also Handle cases like hardware or real-time system interrupts using a queue.
  • It is also used to Handle traffic on various websites.
  • You can use a queue for Routers and switches in networking.
  • Playlist in media players also uses queues for proper functioning.

Let us look at some examples of a queue to understand it better. Consider the following examples:

Example-1:

class QueueExample:

   def __init__(self):

      self.queue = list()

   def addtoque(self,datavalue):

# the following is the Insert method to add an element in the queue

   if datavalue not in self.queue:

      self.queue.insert(0,datavalue)

      return True

   return False

   def size(self):

      return len(self.queue)

TheQueue = QueueExample ()

TheQueue.addtoque(“Monday”)

TheQueue.addtoque(“Tuesday”)

TheQueue.addtoque(“Wednesday”)

print(TheQueue.size())

After executing the above program, you will get the following result as output.

Output:  3

The above example program explains to you the process of adding the elements in a queue. Now, let us look at another example program that tells you the process of removing the elements in a queue.

Example-2:

class QueueExample:

   def __init__(self):

      self.queue = list()

   def addtoque(self,datavalue):

# the following is the Insert method to add an element in the queue

   if datavalue not in self.queue:

      self.queue.insert(0,datavalue)

      return True

   return False

# the following is the pop method to remove an element in the queue

   def removefromque(self):

      if len(self.queue)>0:

         return self.queue.pop()

      return (“There are no elements found in the Queue!”)

TheQueue = QueueExample()

TheQueue.addtoque(“Mon”)

TheQueue.addtoque(“Tue”)

TheQueue.addtoque(“Wed”)

print(TheQueue.removefromque())

print(TheQueue.removefromque())     

return len(self.queue)

After executing the above program, you will get the following result as output.

Monday

Tuesday

Differences Between a Stack and a Queue

Till now, you have learned the basic information and details about both stack and a queue. Now, it’s time to know the difference between a stack and a queue. So, consider the following differences between them.

1) Basics:

However both a Stack and a queue are the linear data structures, but the objects in the stack are removed or inserted at the same end whereas the objects in the queue are removed and inserted from two different ends. This is the basic information of a Stack and a Queue in programming.

2) Working Principle:

The working principle followed by the stack is the Last In, First Out (LIFO) principle. According to this principle, you find that the last inserted element will be deleted first. But the working principle of a queue is the First In, First Out (FIFO) principle. According to this principle, the elements that are added first get removed first from the list.

3) Pointers :

There is only one pointer at the top of the stack that indicates the address of the topmost element or the last inserted one of the stack whereas in the queue, the front pointer indicates the address of the first inserted element in a queue.

4) Operations:

There are two operations used by Stack named push and pop operations. You can use the pop operation functions to remove the element from the list and the push operation functions to insert the element into a list. But in the case of Queue, the two operations are en queue and de queue operations. The elements from the queue can be removed with the help of the dequeue operation, and you can insert the elements in a queue with the help of enqueue operation.

5) Full Condition Examination:

When top== max-1, it means that the stack is full.    When rear==max-1, it means that the queue is full.

6) Empty Condition Examination:

When top==-1, it indicates that the stack is empty. When front = rear+1 or front== -1, it indicates that the queue is empty.

7) Variants:

A Stack data structure does not have any types. A Queue data structure has three types- circular queue, priority queue, and double-ended queue.

8) Visualization:

You can visualize the Stack as a vertical collection whereas a queue can be visualized as a horizontal collection.

9: Implementation:

The implementation is simpler in a Stack whereas the implementation in a queue is comparatively more complex than in a stack.

Therefore, these are the top differences between a Stack and Queue in programming. It is important to know the differences between them because with that you will come to know where to use them.

Also, check

Java: Float vs Double.

How to Compare Strings in Python? – Everything About String Comparison

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