Question 1

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 2

How do you rotate an N×N matrix by 90 degrees in place?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews — you only need Python lists of lists and nested loops.
**Difficulty:** Medium
**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 word an interviewer expects. Every program here was run with `python3`, and the output shown in the **Verified** section is copied from that run.

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

You ar

Question 3

How do you search a sorted 2D matrix?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews — you should know arrays, nested lists and loops; binary search is linked and summarised.
**Difficulty:** Medium
**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, step count and ordering claim below was produced by actually running the Python programs in the **Verified** secti

Question 4

How do you traverse a matrix in spiral order?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews — you only need Python lists of lists, `range` and `while` loops.
**Difficulty:** Medium
**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 word an interviewer expects. Every program here was run with `python3`, and the output shown in the **Verified** section is copied from that run.

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

Question 5

How does the Floyd-Warshall algorithm work?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews — no graph-algorithm background assumed
**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 Matters — A Story First

Old ro

Question 6

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

DATA STRUCTURES & ALGORITHMSDECODED.

Easy