Algorithm Atlas

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Learn Stack with visual DSA lessons

Learn Stack with 7 DSA patterns and 32 visual lessons. Follow step-by-step animations and synced C#, Python, and Java code.

A stack is a pile where the newest item is removed first.

Monotonic Stack

Keep values increasing or decreasing to reveal the next useful neighbor.

Next Greater Element I Easy · LIFO state
Next Greater Element II Medium · LIFO state
Daily Temperatures Medium · LIFO state
Online Stock Span Medium · LIFO state
Asteroid Collision Medium · LIFO state
Largest Rectangle in Histogram Hard · LIFO state
Maximal Rectangle Hard · LIFO state

Expression Evaluation

Use a stack to remember unfinished numbers, operators, and bracket groups.

Basic Calculator II Medium · LIFO state
Evaluate Reverse Polish Notation Medium · LIFO state
Decode String Medium · LIFO state
Basic Calculator I Hard · LIFO state

Stack Simulation / Undo Operation

Push normal actions and pop when an undo or removable pair appears.

Backspace String Compare Easy · LIFO state
Remove All Adjacent Duplicates Easy · LIFO state
Make the String Great Easy · LIFO state
Minimum String Length After Removing Substrings Medium · LIFO state

Parenthesis & Scoring

Match each closing bracket with the newest unmatched opening bracket.

Valid Parentheses Easy · LIFO state
Minimum Add to Make Parentheses Valid Medium · LIFO state
Score of Parentheses Medium · LIFO state
Longest Valid Parentheses Hard · LIFO state

Stack-Based Design

Combine stacks or queues and store extra information beside each value.

Implement Queue using Stacks Easy · LIFO state
Implement Stack using Queues Easy · LIFO state
Min Stack Medium · LIFO state
Max Stack Medium · LIFO state
Design Stack with Increment Operation Medium · LIFO state

Stack + Greedy

Remove the newest choice whenever a better choice arrives.

Remove K Digits Medium · LIFO state
Remove Duplicate Letters Medium · LIFO state
Smallest Subsequence of Distinct Characters Medium · LIFO state
Minimum Remove to Make Valid Parentheses Medium · LIFO state
Create Maximum Number Hard · LIFO state

Recursive Stack

Remove the top, solve the smaller stack, then rebuild it.

Delete Middle Element of Stack Easy · LIFO state
Reverse a Stack (Recursive) Medium · LIFO state
Insert at Bottom of Stack Medium · LIFO state