Question 1

How do you validate that a binary tree is a BST?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews — you should know what a binary tree and recursion are.  
**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

Question 2

What is a greedy algorithm?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews — you should know lists, loops and functions in Python; everything else is explained.  
**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

Question 3

How do you merge overlapping intervals?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews — you need loops, lists/arrays and sorting in Python.  
**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 yo

Question 4

How do you find the minimum number of meeting rooms required?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews — you need sorting and arrays in Python; heaps 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, and

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

DATA STRUCTURES & ALGORITHMSDECODED.

Medium

How do you validate that a binary tree is a BST?

What is a greedy algorithm?

How do you merge overlapping intervals?

How do you find the minimum number of meeting rooms required?

Hard

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