Question 1

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 2

How do you solve the coin change problem?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews — you need loops, arrays and a first idea of what dynamic programming is.  
**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 ru

Question 3

How do you design an LRU cache?

Accepted Answer

**Target Audience:** Developers preparing for coding and system design interviews who know maps and classes in Python.  
**Difficulty:** Hard  
**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 yo

Question 4

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

Accepted Answer

**Target Audience:** Interview candidates who know recursion and grid DFS; memoisation and the DAG view 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 Mat

Question 5

Burst Balloons: why does DP over intervals (not balloons) work?

Accepted Answer

**Target Audience:** Interview candidates who have seen basic dynamic programming (a 1-D table) and want to learn interval DP — every new idea is explained  
**Difficulty:** Hard  
**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 pag

Question 6

Design an LRU Cache with O(1) get and put — why doubly linked list + hash map?

Accepted Answer

**Target Audience:** Developers preparing for coding interviews who know classes and references in Python and want to justify the LRU design, not just recite it.  
**Difficulty:** Hard  
**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 th

DATA STRUCTURES & ALGORITHMSDECODED.

Easy