leetcode/apps/docs/content/(01-linear-structures)/stack/index.mdx

---
title: Stack
description: 'Items are added and removed from one end, so the last item added is the first item removed.'
hidden: true
---

A stack works like a stack of plates in a cafeteria. You add new plates on top. When you need a plate, you take from the top. The last plate you added is the first one you remove.

This is **Last-In-First-Out (LIFO)**. The most recent item goes out first.

![](../../../public/stack-plates-metaphor.svg)

## Core Stack Operations

A stack has two fundamental operations:

- **Push**: add an item to the top of the stack
- **Pop**: remove the item at the top of the stack

Some stacks have additional operations:

- **Peek**: get the item at the top of the stack without removing it
- **IsEmpty**: check if the stack is empty

![](../../../public/stack-operations-sequence.svg)

```python
# Using Python list as a stack
stack = []

# Push elements
stack.append(10)
stack.append(20)
stack.append(30)
# Stack: [10, 20, 30] (30 is on top)

# Pop element
top = stack.pop()  # Returns 30
# Stack: [10, 20]

# Peek at top
if stack:
    top_element = stack[-1]  # Returns 20 without removing
```

Python lists provide `append()` for pushing and `pop()` for popping. The `peek()` method is not built-in, but you can implement it yourself.

## Last in, First out

The defining characteristic of a stack is LIFO order. Whatever you put in last comes out first. This is different from a queue, which is First-In-First-Out (FIFO).

Add items: A, B, C

- Stack: [A, B, C] (C on top)

Remove items:

- First pop: C
- Second pop: B
- Third pop: A

The order reverses. Items come out in the opposite order they went in.