STACK DATA STRUCTURE

What is a stack?

• A stack is an abstract data type that holds an ordered, linear sequence of items

• A stack is a last in, first out (LIFO) structure

• A real-life example is a stack of plates:

  • You can only take a plate from the top of the stack, and you can only add a plate to the top of the stack

  • If you want to reach a plate that is not on the top of the stack, you need to remove all of the plates that are above that one

  • In a stack data structure, you can only access the element on the top of the stack

  • The element that was added last will be the one to be removed first

  • To implement a stack, you need to maintain a pointer to the top of the stack (the last element to be added)

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What are the operations of a stack?

• The main stack operations are:​​​​​​​

  • push(data) - adds an element to the top of the stack

  • pop( ) - removes an element from the top of the stack

  • peek( ) - returns a copy of the element on the top of the stack without removing it

  • is_empty( ) - checks whether a stack is empty

  • is_full( ) - checks whether a stack is at maximum capacity when stored in a static (fixed-size) structure

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How does a stack work?

• Below is a visualisation of how a stack works