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

What is Big-O notation?

Accepted Answer

**Target Audience:** Complete beginners preparing for coding interviews — no maths beyond multiplication assumed.
**Difficulty:** Easy
**Language:** Python 3

> **How to read this doc:** Every idea is explained in plain words first, then tagged with `📌 Interview term:` so you also learn the exact vocabulary an interviewer expects. Every number on this page (step counts, comparisons, overflow values) comes from actually running the Python code shown, and the **Verified** section quotes that outp

Question 3

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 4

What is space complexity, and how much stack space does recursion use?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews — you should know what a function call and a loop are.
**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 depth, count and error message on this page comes from running the Python code shown; the **Verified** section quotes that output. This page assumes you know

Question 5

How should you approach a DSA problem in a coding interview?

Accepted Answer

**Target Audience:** Anyone preparing for their first coding interviews — no prior algorithms knowledge assumed.
**Difficulty:** Easy
**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 program in this doc was run with `python3 main.py`, and the output quoted in the **Verified** section is copied from that run.

## 1. Why This Even Matters — A Stor

Question 6

How do you check if two strings are anagrams?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews — you know Python strings, loops and dicts; nothing else 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 output shown was produced by running the code with `python3` (3.13); nothing is typed in by hand.

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

Two

Question 7

How do you solve the Two Sum problem efficiently?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews — you know basic Python lists and loops; nothing else 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 output shown was produced by actually running the code with `python3` (3.13); nothing is typed in by hand.

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

Question 8

How do you find the k closest points to the origin?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews — you need Python lists, tuples and loops; heaps are explained on the linked page.  
**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 ac

Question 9

How do you implement a queue using two stacks?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews; you should know what a stack is.
**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 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

A bakery has a tall, narrow tray ra

Question 10

How do you generate all subsets of an array?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews — you should know arrays and basic 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 output you see in

DATA STRUCTURES & ALGORITHMSDECODED.

Easy

How does binary search work and what are its requirements?

What is Big-O notation?

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

What is space complexity, and how much stack space does recursion use?

How should you approach a DSA problem in a coding interview?

How do you check if two strings are anagrams?

How do you solve the Two Sum problem efficiently?

Medium

How do you find the k closest points to the origin?

How do you implement a queue using two stacks?

How do you generate all subsets of an array?

How do you solve the Combination Sum problem?

Implement Trie for autocomplete — how do you handle wildcards (.)?

How do you generate all permutations of an array?

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

What is binary search on the answer?

Hard

Sliding window median: how do you maintain median with two heaps as the window slides?

How do you merge k sorted lists?

How do you solve the word ladder problem?

Alien Dictionary: given sorted words in an alien language, how do you derive the character order?

How do you solve the N-Queens problem?

How does Dijkstra's algorithm work?