ARRAYS | Full DSA Guide + 5 LeetCode Problems in Python

Elephants never forget, and neither does memory. 🐘 In this Big O Zoo episode, Ellie the Elephant takes you inside your computer's memory to show what an array really is, why arr[i] is instant but insert(0, x) is slow, how Python lists secretly resize themselves (amortized O(1)!), and then we solve 5 of the most-asked array interview questions at big tech companies, step by step, in Python. 🧠 What you'll learn What an array is: contiguous memory, same-size slots, addresses Why indexing is O(1) (the address formula) and why we count from 0 Search, insert, delete: what's O(1), what's O(n), and why Dynamic arrays & amortized O(1) append (how Python lists grow) Python list cheat sheet (slicing, pop(0), "in", sort…) 2D arrays, row-major order, and the [[0]*3]*3 trap 5 interview patterns that unlock hundreds of problems 🧩 Problems solved (Python) 1️⃣ Two Sum (LeetCode 1): Hash map 2️⃣ Best Time to Buy and Sell Stock (LeetCode 121): Running minimum 3️⃣ Container With Most Water (LeetCode 11): Two pointers 4️⃣ Maximum Subarray (LeetCode 53): Kadane's algorithm 5️⃣ Product of Array Except Self (LeetCode 238): Prefix & suffix 📝 Homework Contains Duplicate (217) • Two Sum II (167) • Subarray Sum Equals K (560) • Trapping Rain Water (42) ⏱️ Chapters 0:00 Intro 0:29 Welcome to the Zoo 1:12 What is an array? 2:35 Indexing & O(1) access 4:13 Searching: O(n) 5:11 Inserting: O(1) vs O(n) 6:28 Deleting 7:04 Array scorecard 7:30 Dynamic arrays & amortized O(1) 9:44 Python list cheat sheet 10:34 2D arrays (+ a Python trap) 11:48 The 5 interview patterns 12:39 Problem 1: Two Sum (hash map) 15:05 Two Sum: walkthrough 15:54 Two Sum: code & complexity 17:13 Problem 2: Best Time to Buy & Sell Stock 18:50 Stock: walkthrough 19:35 Stock: code & complexity 20:28 Problem 3: Container With Most Water 22:16 Water: walkthrough 23:11 Water: code & complexity 23:53 Problem 4: Maximum Subarray (Kadane) 25:23 Kadane: walkthrough 26:22 Kadane: code & complexity 27:10 Problem 5: Product of Array Except Self 28:53 Product: walkthrough 29:57 Product: code & complexity 30:48 Recap: patterns & clues 31:35 Pop quiz 32:21 Homework & outro 🐾 Meet the residents: Ellie the Elephant (memory), Pip & Tweet the lovebirds (hash map), Foxy (running min), Pinchy the crab (two pointers), Kanga (Kadane's), Nutsy the squirrel (prefix/suffix) 👉 Next enclosure: Linked Lists. Subscribe so you don't miss it! #DSA #Arrays #LeetCode #CodingInterview #Python #BigO #DataStructures #Algorithms