Question 1

How do you find the intersection node of two linked lists?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews — you should know what a linked list node is; everything else is explained
**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 in the **Verified** section was copied from a real run of the examples on this page.

## 1. Why This E

Question 2

How do you merge two sorted linked lists?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews — no prior algorithms knowledge 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 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

Two te

Question 3

What is a stable sorting algorithm?

Accepted Answer

**Target Audience:** Beginners who know what sorting is and want to understand the guarantees behind it.
**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 Story First

Question 4

How do you merge two sorted arrays?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews — you only need to know Python lists and loops.
**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 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

Two teachers hav

Question 5

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 6

How do merge sort and quicksort work?

Accepted Answer

# How Merge Sort and Quicksort Work (Python)

**Target Audience:** Beginners preparing for coding interviews; basic loops, arrays and functions are enough.
**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

Question 7

Merge k sorted lists: heap vs divide-and-conquer — which is better for n=10k?

Accepted Answer

**Target Audience:** Developers who know basic arrays and loops in Python and want to reason about algorithm trade-offs, not just Big-O.  
**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 ru

Question 8

Compare common sorting algorithms.

Accepted Answer

# Comparing Common Sorting Algorithms (Python)

**Target Audience:** Beginners preparing for coding interviews; you only need to know what an array and a loop are.
**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

Question 9

What is the Union-Find (Disjoint Set) data structure?

Accepted Answer

**Target Audience:** Beginners preparing for coding interviews — you should know what an array is; everything else is explained
**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 Matt

Question 10

How do you merge k sorted lists?

Accepted Answer

**Target Audience:** Intermediate — you should know Python classes and how a singly linked list works; heaps are explained on the linked page.  
**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 page was actuall

DATA STRUCTURES & ALGORITHMSDECODED.

Easy

How do you find the intersection node of two linked lists?

How do you merge two sorted linked lists?

What is a stable sorting algorithm?

How do you merge two sorted arrays?

Medium

How do you merge overlapping intervals?

How do merge sort and quicksort work?

Merge k sorted lists: heap vs divide-and-conquer — which is better for n=10k?

Compare common sorting algorithms.

What is the Union-Find (Disjoint Set) data structure?

Hard

How do you merge k sorted lists?

Count of smaller numbers after self with Fenwick tree — how to coordinate compress?

What is a segment tree and when do you need one?

Median of two sorted arrays in O(log(min(m,n))) — how does the partition trick work?

Design Twitter feed: how do you fan-out with heap + hash for timeline?