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Medium Roadmap

The core of FAANG interviews.

Introduction

"Medium" LeetCode questions make up roughly 80% of the questions asked in FAANG onsite interviews.

They are the perfect balance: they require you to combine 2 or 3 fundamental concepts from the Easy tier, but they don't require obscure, esoteric algorithms.

The Goals of Medium Questions

  1. Pattern Recognition: You read a prompt and immediately know it's a "Sliding Window" or "Topological Sort" problem.
  2. Trade-off Analysis: You can discuss whether to optimize for Time or Space.
  3. Graph and Tree Mastery: You are completely comfortable traversing complex non-linear structures.

The Medium Patterns to Master

You should spend the vast majority of your prep time here. Aim to solve these in 20-30 minutes.

1. Sliding Window

Maintaining a dynamic subset of contiguous elements. - Classic Problem: Longest Substring Without Repeating Characters (LeetCode 3) - Classic Problem: Best Time to Buy and Sell Stock (LeetCode 121 - Note: technically easy, but sliding window concept)

2. Fast & Slow Pointers (Floyd's Tortoise and Hare)

Using pointers that move at different speeds to find cycles or midpoints. - Classic Problem: Linked List Cycle (LeetCode 141) - Classic Problem: Find the Duplicate Number (LeetCode 287)

3. Backtracking

Generating combinations, permutations, and subsets by exploring and undoing state. - Classic Problem: Subsets (LeetCode 78) - Classic Problem: Combination Sum (LeetCode 39)

4. Graph Traversals (BFS & DFS on Matrices)

Treating a 2D grid as a graph and exploring islands or paths. - Classic Problem: Number of Islands (LeetCode 200) - Classic Problem: Rotting Oranges (LeetCode 994)

5. Top K Elements (Heaps)

Using a Priority Queue to maintain the largest or smallest elements efficiently. - Classic Problem: Top K Frequent Elements (LeetCode 347) - Classic Problem: Kth Largest Element in an Array (LeetCode 215)

6. Intervals

Sorting arrays of start/end times and merging overlapping segments. - Classic Problem: Merge Intervals (LeetCode 56) - Classic Problem: Insert Interval (LeetCode 57)

7. 1D Dynamic Programming

Caching overlapping subproblems in an array (Tabulation) or Dictionary (Memoization). - Classic Problem: Climbing Stairs (LeetCode 70) - Classic Problem: Coin Change (LeetCode 322)

When are you ready for Hards?

You are ready for Hards when: - You can implement BFS and DFS on a matrix in under 5 minutes without thinking. - You can write a standard Backtracking template perfectly from memory. - You immediately recognize when to use a Heap vs sorting the entire array.