Question 1

What is the time complexity of common operations on arrays, hash maps, and balanced trees?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews — you should know what a list and a loop are; everything else is explained.
**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 count on this page (shifts, comparisons, tree heights) comes from running the Python code shown, and the **Verified** section quotes tha

Question 2

What is a binary search tree (BST)?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews — you only need to know what a variable, a loop and a function are.  
**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 t

Question 3

How do you check if a root-to-leaf path sums to a target?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews; you should know what a binary tree is.
**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 words an interviewer expects. Every code block in this Python version was run, and the **Verified** section quotes the real output.

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

You are on a hike with a fixed

Question 4

How do you invert a binary tree?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews; you should know what a binary tree is.
**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 words an interviewer expects. Every code block in this Python version was run, and the **Verified** section quotes the real output.

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

Hold a printed organisation cha

Question 5

How do you check if a binary tree is symmetric?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews; you should know what a binary tree is.
**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 words an interviewer expects. Every code block in this Python version was run, and the **Verified** section quotes the real output.

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

Fold a sheet of paper in half,

Question 6

What are the tree traversal methods?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews; no prior knowledge of trees 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 words an interviewer expects. Every code block in this Python version was run, and the **Verified** section quotes the real output.

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

Imagine you have just moved into

Question 7

How do you find the maximum depth of a binary tree?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews; you should know what a binary tree is.
**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 words an interviewer expects. Every code block in this Python version was run, and the **Verified** section quotes the real output.

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

Picture a family tree drawn on

Question 8

How do you find the lowest common ancestor in a binary tree?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews — you should know what a binary tree and a recursive function are; 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 th

Question 9

How do you check if a binary tree is balanced?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews — you should know what a binary tree and a recursive function are; 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 th

Question 10

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

DATA STRUCTURES & ALGORITHMSDECODED.

Easy

What is the time complexity of common operations on arrays, hash maps, and balanced trees?

What is a binary search tree (BST)?

How do you check if a root-to-leaf path sums to a target?

How do you invert a binary tree?

How do you check if a binary tree is symmetric?

What are the tree traversal methods?

How do you find the maximum depth of a binary tree?

Medium

How do you find the lowest common ancestor in a binary tree?

How do you check if a binary tree is balanced?

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

How do you get the right-side view of a binary tree?

How do you compute the diameter of a binary tree?

How do you find the kth smallest element in a BST?

How do you do a level-order (BFS) traversal of a tree?

How do you build a binary tree from preorder and inorder traversals?

Hard

How do you serialize and deserialize a binary tree?