Question 1

What is topological sort and when is it used?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews — no prior algorithms knowledge assumed
**Difficulty:** Medium
**Language:** Python 3

> **How to read this doc:** Every idea is explained in plain language first, then tagged with `📌 Interview term:` so you also learn the exact word an interviewer expects. All code is Python, and every output block in the **Verified** section was copied from a real run of the examples on this page.

## 1. Why This Even Matters — A Story First

Thin

Question 2

How do you solve the course schedule (prerequisites) problem?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews — no prior algorithms knowledge assumed
**Difficulty:** Medium
**Language:** Python 3

> **How to read this doc:** Every idea is explained in plain language first, then tagged with `📌 Interview term:` so you also learn the exact word an interviewer expects. All code is Python, and every output block in the **Verified** section was copied from a real run of the examples on this page.

## 1. Why This Even Matters — A Story First

You

Question 3

What is the difference between BFS and DFS?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews — you should know what a graph and an adjacency list are  
**Difficulty:** Medium  
**Language:** Python 3

> **How to read this doc:** every idea is explained in plain words first. When a word appears that an interviewer will expect you to know, it is tagged `📌 Interview term:` with a one-line definition, and every tagged term is collected in the Quick Glossary at the end. Every program on this page was actually run, and the output

Question 4

Course Schedule: detect cycle with topological sort (Kahn vs DFS)?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews — no prior algorithms knowledge assumed
**Difficulty:** Medium
**Language:** Python 3

> **How to read this doc:** Every idea is explained in plain language first, then tagged with `📌 Interview term:` so you also learn the exact word an interviewer expects. All code is Python, and every output block in the **Verified** section was copied from a real run of the examples on this page.

## 1. Why This Even Matters — A Story First

Two

Question 5

Longest increasing path in matrix — why DFS + memo beats brute force?

Accepted Answer

**Target Audience:** Interview candidates who know recursion and grid DFS; memoisation and the DAG view are explained from scratch
**Difficulty:** Hard
**Language:** Python 3

> **How to read this doc:** Every idea is explained in plain language first, then tagged with `📌 Interview term:` so you also learn the exact word an interviewer expects. All code is Python, and every output block in the **Verified** section was copied from a real run of the examples on this page.

## 1. Why This Even Mat

Question 6

Alien Dictionary: given sorted words in an alien language, how do you derive the character order?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews — no prior algorithms knowledge assumed
**Difficulty:** Hard
**Language:** Python 3

> **How to read this doc:** Every idea is explained in plain language first, then tagged with `📌 Interview term:` so you also learn the exact word an interviewer expects. All code is Python, and every output block in the **Verified** section was copied from a real run of the examples on this page.

## 1. Why This Even Matters — A Story First

Archae

Question 7

How do you find strongly connected components in a directed graph?

Accepted Answer

**Target Audience:** Interview candidates who know BFS and DFS on graphs; strongly connected components are explained from scratch
**Difficulty:** Hard
**Language:** Python 3

> **How to read this doc:** Every idea is explained in plain language first, then tagged with `📌 Interview term:` so you also learn the exact word an interviewer expects. All code is Python, and every output block in the **Verified** section was copied from a real run of the examples on this page.

## 1. Why This Even Mat

DATA STRUCTURES & ALGORITHMSDECODED.

Medium

What is topological sort and when is it used?

How do you solve the course schedule (prerequisites) problem?

What is the difference between BFS and DFS?

Course Schedule: detect cycle with topological sort (Kahn vs DFS)?

Hard

Longest increasing path in matrix — why DFS + memo beats brute force?

Alien Dictionary: given sorted words in an alien language, how do you derive the character order?

How do you find strongly connected components in a directed graph?