Stacks and Queues

Stacks

A stack is a data structure that consists of nodes, each node has a value and pointer that points to the next node.

Stacks follow the following two principles:

• LIFO (Last In First Out), this means that the last element added to the stack will be the first element popped out of the stack.
• FILO (First In Last Out), this means that the first element added to the stack will be the last element pooped ou of the stack.

A stack must implement the following methods:

1. push(Node node) method that pushes the elements to the stack
2. pop() method that pops the last element added to the stack(the popped element will be removed from the stack)
3. peek() method that returns the top element of the stack without removing it (*just view the top element)
4. isEmpty() returns true if the stack is empty and false if it is not.

and the stack also has a variable called top that keeps pointing to the last element pushed to the stack.

Queues

A queue is also a data structure that consists of nodes, each node has a value and a pointer that points to the next node.

Queues follow the following principles:

• FIFO (First In First Out), this means that the first element that entered the queue will be the first element to go out.
• LILO (Last In Last Out), this means that the last element that entered the queue will be the last element to go out.

A queue must implement the following methods:

1. enqueue(Node node) method that adds a node to the queue.
2. dequeue() method that returns the first element entered the queue (dequeue method will remove the element from the queue)
3. peek() method that views the front (the first element entered the queue) without removing it from the queue.
4. isEmpty() method that returns true if the queue is empty else it will return false

and the queue also has a variable called front that points to the first element entered the queue, and another variable called rare that points to the last element added to the queue.