Question 1

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 2

Number of islands with DFS vs BFS vs Union-Find — trade-offs?

Accepted Answer

**Target Audience:** Candidates who can already solve number of islands once and want to compare the three standard approaches  
**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

Question 3

What is the Union-Find (Disjoint Set) data structure?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews — you should know what an array is; everything else is explained
**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 Matt

Question 4

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

Accepted Answer

**Target Audience:** Interview candidates who know what a graph and a heap are; minimum spanning trees 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 Matt

DATA STRUCTURES & ALGORITHMSDECODED.

Medium

How do you count connected components in an undirected graph?

Number of islands with DFS vs BFS vs Union-Find — trade-offs?

What is the Union-Find (Disjoint Set) data structure?

Hard

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