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

What is space complexity, and how much stack space does recursion use?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews — you should know what a function call and a loop are.
**Difficulty:** Easy
**Language:** Python 3

> **How to read this doc:** Each idea is explained in plain words first, then tagged with `📌 Interview term:` so you also learn the exact vocabulary an interviewer expects. Every depth, count and error message on this page comes from running the Python code shown; the **Verified** section quotes that output. This page assumes you know

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 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 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

Implement Trie for autocomplete — how do you handle wildcards (.)?

Accepted Answer

**Target Audience:** Developers who know what a trie is and want the classic design question — you need recursion and basic classes.  
**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, a

Question 9

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 10

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

DATA STRUCTURES & ALGORITHMSDECODED.

Easy

What is the difference between a stack and a queue?

What is space complexity, and how much stack space does recursion use?

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 detect a cycle in a directed graph?

How do you check if a graph is bipartite?

Implement Trie for autocomplete — how do you handle wildcards (.)?

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

How do you count connected components in an undirected graph?

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

Hard

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

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