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# Stack

> Structure with limited access to data.
>
> L.I.F.O. ( Last In First Out ) Structure

## How it works?

* You keep putting elements on top
* You have easy access to remove or look at the top element

![](/files/-MSZw11YJIKEGvG123B-)

## When to use?

* when you only care about the most recent elements
* the order in which you see & save elements actually matters

## Push & Pop

1. Push

   : when you add an element to a stack

   -> O(1)
2. Pop

   : when you taken an element off of the stack

   -> O(1)

   \=> All you need here is to look at the top element of the stack!

## Stack in Python

* `pop()` is a given function
* `append()` is equivalent to a push function

Make your own code instead of using `append()` since it traverses the whole list, taking O(n)

-> it will take a lot faster if we push/pop from the first element in a linked list!


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