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Easy Roadmap

Building your fundamental muscle memory.

Introduction

"Easy" LeetCode questions are rarely asked in FAANG onsite loops (they might appear as a warm-up in a phone screen). However, you must master them because they form the atomic building blocks of Medium and Hard questions.

If you struggle with an Easy question, it means you have a gap in your knowledge of a core Data Structure.

The Goals of Easy Questions

  1. Language Fluency: You should be able to write for loops, initialize dictionaries, and slice arrays in Python without thinking about the syntax.
  2. Edge Case Awareness: Learning to handle empty arrays, single-element arrays, and negative numbers.
  3. Complexity Intuition: Realizing why your nested for loop (Brute Force) is too slow, and learning how a Hash Map fixes it.

The Easy Patterns to Master

Do not move on to Medium questions until you can comfortably solve these Easy patterns in under 15 minutes:

1. Hash Maps (Counting & Lookups)

The ability to map a key to a value in \(O(1)\) time is the most important skill in interviewing. - Classic Problem: Two Sum (LeetCode 1) - Classic Problem: Valid Anagram (LeetCode 242)

2. Two Pointers (Opposite Ends)

Moving a left and right pointer towards the center of an array or string. - Classic Problem: Valid Palindrome (LeetCode 125)

3. Linked List Traversal

Understanding how to move a pointer curr = curr.next without losing the head. - Classic Problem: Reverse Linked List (LeetCode 206) - Classic Problem: Merge Two Sorted Lists (LeetCode 21)

4. Binary Search (Basic)

Finding a target in a sorted array in \(O(\log N)\) time. - Classic Problem: Binary Search (LeetCode 704)

5. Depth-First Search (Tree Traversal)

Understanding basic recursive calls on root.left and root.right. - Classic Problem: Maximum Depth of Binary Tree (LeetCode 104) - Classic Problem: Invert Binary Tree (LeetCode 226)

When are you ready for Mediums?

You are ready for Mediums when: - You know exactly when to use a Dictionary vs a Set. - You can reverse a Linked List perfectly on the first try without a NoneType error. - You can write a basic Binary Search while left <= right loop from memory. - You can explain the difference between \(O(N)\) and \(O(N^2)\) confidently.