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

In a restaurant ki

Question 2

How do you check if a binary tree is symmetric?

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

Fold a sheet of paper in half,

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

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 5

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 6

How do you implement a queue using two stacks?

Accepted Answer

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

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

A bakery has a tall, narrow tray ra

Question 7

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 8

What is a heap / priority queue?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews — you need Python lists and loops; no tree knowledge assumed.  
**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 o

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

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

DATA STRUCTURES & ALGORITHMSDECODED.

Easy

What is the difference between a stack and a queue?

How do you check if a binary tree is symmetric?

What are the tree traversal methods?

Medium

What is topological sort and when is it used?

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

How do you implement a queue using two stacks?

How do you check if a graph is bipartite?

What is a heap / priority queue?

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?

Hard

How do you serialize and deserialize a binary tree?

How do you solve the word ladder problem?