Question 1

How does binary search work and what are its requirements?

Accepted Answer

# How Binary Search Works and What It Requires (Python)

**Target Audience:** Beginners preparing for coding interviews; you only need to know arrays and loops.
**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 was produced by actually running the programs (Python 3.13.16); nothing is quot

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 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

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Question 4

What is dynamic programming?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews; you should be comfortable with functions, loops and recursion.
**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 out

Question 5

How do you solve the 0/1 knapsack problem?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews — you need loops, lists and 2D lists.  
**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 output you see in the **V

Question 6

How do you solve the Combination Sum problem?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews — you should know recursion and the subsets pattern  
**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 output you

Question 7

Maximum subarray (Kadane) vs divide-and-conquer — proof of correctness?

Accepted Answer

**Target Audience:** Candidates who already know Kadane's algorithm and want to explain why it works and how it compares.
**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 output y

Question 8

How do you search in a rotated sorted array?

Accepted Answer

# Searching a Rotated Sorted Array (Python)

**Target Audience:** Learners who know basic binary search and are preparing for coding interviews.
**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 was produced by actually running the programs (Python 3.13.16); nothing is quoted from memory

Question 9

How do you find the maximum subarray sum?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews; you should know arrays and loops.
**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 output you see in the **Verified

Question 10

How do you count the number of set bits in an integer?

Accepted Answer

**Target Audience:** Developers preparing for coding interviews who know loops and integers in Python; binary is explained as we go.  
**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

DATA STRUCTURES & ALGORITHMSDECODED.

Easy

How does binary search work and what are its requirements?

How do you solve the climbing stairs problem?

Medium

What is topological sort and when is it used?

What is dynamic programming?

How do you solve the 0/1 knapsack problem?

How do you solve the Combination Sum problem?

Maximum subarray (Kadane) vs divide-and-conquer — proof of correctness?

How do you search in a rotated sorted array?

How do you find the maximum subarray sum?

How do you count the number of set bits in an integer?

Hard

How does the Floyd-Warshall algorithm work?

How do you compute the edit distance between two strings?

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

What is bitmask dynamic programming?