Question 1

What is a graph, and how do you represent it?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews — no graph knowledge needed, just arrays and loops  
**Difficulty:** Easy  
**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 you see

Question 2

How do you find the longest common prefix of an array of strings?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews — no prior algorithms knowledge assumed
**Difficulty:** Easy
**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

A libr

Question 3

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 4

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 5

How do you detect a cycle in a directed graph?

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

Pict

Question 6

How do you check if a graph is bipartite?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews — you know Python lists and loops; graphs and colouring are explained from scratch.
**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 words an interviewer expects. Every output shown was produced by actually running the code with `python3` (3.13); nothing is typed in by hand.

## 1. Why This Even

Question 7

How do you generate all permutations of an array?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews — you should know arrays and basic recursion  
**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 you see in

Question 8

How do you count connected components in an undirected graph?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews — you should know what an adjacency list is and roughly how BFS or DFS work  
**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

Question 9

When would you use BFS over Dijkstra for shortest paths?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews — no graph-algorithm background 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 10

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

DATA STRUCTURES & ALGORITHMSDECODED.

Easy

What is a graph, and how do you represent it?

How do you find the longest common prefix of an array of strings?

Medium

What is topological sort and when is it used?

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

How do you detect a cycle in a directed graph?

How do you check if a graph is bipartite?

How do you generate all permutations of an array?

How do you count connected components in an undirected graph?

When would you use BFS over Dijkstra for shortest paths?

What is the difference between BFS and DFS?

Hard

How does the Floyd-Warshall algorithm work?

How does the Bellman-Ford algorithm work?

How do you solve the word ladder problem?

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

What is the difference between Kruskal's and Prim's MST algorithms?

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

How does Dijkstra's algorithm work?