Question 1

How do you reverse a linked list?

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

Pictur

Question 2

How do you solve the climbing stairs problem?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews; this is usually the first dynamic programming problem people meet.
**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 o

Question 3

What is the difference between an array and a linked list?

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

Picture two ways o

Question 4

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 5

What is Big-O notation?

Accepted Answer

**Target Audience:** Complete beginners preparing for coding interviews — no maths beyond multiplication assumed.
**Difficulty:** Easy
**Language:** Python 3

> **How to read this doc:** Every idea is explained in plain words first, then tagged with `📌 Interview term:` so you also learn the exact vocabulary an interviewer expects. Every number on this page (step counts, comparisons, overflow values) comes from actually running the Python code shown, and the **Verified** section quotes that outp

Question 6

How do you find the intersection node of two linked lists?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews — you should know what a linked list node is; everything else is explained
**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 E

Question 7

How do you find the missing number in 0..n?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews — you should know what an array and a loop are; nothing else is 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 output shown in the **Verified** section was produced by actually running the Python code with `python3 main.py`; nothing is quoted from memo

Question 8

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 9

What is recursion and what is a base case?

Accepted Answer

**Target Audience:** Complete beginners preparing for coding interviews — you only need to know what a function is.
**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 trace, count and error message on this page comes from running the Python code shown, and the **Verified** section quotes that output.

## 1. Why This Even Mat

Question 10

How should you approach a DSA problem in a coding interview?

Accepted Answer

**Target Audience:** Anyone preparing for their first coding interviews — no prior algorithms 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 Stor

DATA STRUCTURES & ALGORITHMSDECODED.

Easy

How do you reverse a linked list?

How do you solve the climbing stairs problem?

What is the difference between an array and a linked list?

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

What is Big-O notation?

How do you find the intersection node of two linked lists?

How do you find the missing number in 0..n?

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

Medium

What is dynamic programming?

What is a trie and when is it useful?

Find the kth largest element in an array

How do you find the node where a linked list cycle begins?

What is the difference between BFS and DFS?

How do you solve the word break problem?

How do you detect a cycle in a linked list?

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

Hard

How do you design an LRU cache?

How do you merge k sorted lists?

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