Question 1

What is the difference between a stack and a queue?

Accepted Answer

**Target Audience:** Beginners learning data structures — no prior knowledge assumed.
**Difficulty:** Easy
**Language:** Python 3

> **How to read this doc:** Each idea is explained in plain language first, then tagged with `📌 Interview term:` so you also learn the exact words an interviewer expects. Every program in this doc was run with `python3 main.py`, and the output quoted in the **Verified** section is copied from that run.

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

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Question 2

How do you invert a binary tree?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews; you should know what a binary tree is.
**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 words an interviewer expects. Every code block in this Python version was run, and the **Verified** section quotes the real output.

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

Hold a printed organisation cha

Question 3

What are the tree traversal methods?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews; no prior knowledge of trees 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 words an interviewer expects. Every code block in this Python version was run, and the **Verified** section quotes the real output.

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

Imagine you have just moved into

Question 4

How do you find the maximum depth of a binary tree?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews; you should know what a binary tree is.
**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 words an interviewer expects. Every code block in this Python version was run, and the **Verified** section quotes the real output.

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

Picture a family tree drawn on

Question 5

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 6

How do you get the right-side view of a binary tree?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews — you should know what a binary tree is; BFS and DFS are explained here.  
**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

Question 7

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 8

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

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Question 9

How do you do a level-order (BFS) traversal of a tree?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews — you should know what a binary tree is; queues and BFS are explained here.  
**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 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 the difference between a stack and a queue?

How do you invert a binary tree?

What are the tree traversal methods?

How do you find the maximum depth of a binary tree?

Medium

How do you check if a graph is bipartite?

How do you get the right-side view of a binary tree?

How do you count connected components in an undirected graph?

When would you use BFS over Dijkstra for shortest paths?

How do you do a level-order (BFS) traversal of a tree?

What is the difference between BFS and DFS?

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

How do you solve the Rotting Oranges problem with multi-source BFS?

Hard

How do you serialize and deserialize a binary tree?

How do you solve the word ladder problem?

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