Grokking 75: Top Coding Interview Questions

What it covers

The course is text-based with in-browser coding playgrounds. The course page lists 19 chapters, 184 lessons, 203 playgrounds and a study time of about 25 hours (September 2026). The 75 questions are spread across 18 topic areas so no single topic swallows your preparation:

• Arrays and strings, two pointers, sliding window and matrix problems
• Hash maps and sets, linked lists, stacks and monotonic stacks
• Trees from four angles: depth first search, breadth first search, general binary tree work, and tries
• Graphs, then graph traversal as a separate chapter
• Heaps and priority queues
• Backtracking, dynamic programming, intervals, and divide and conquer

Each topic opens with a short introduction to the structure or pattern, and some include notes on using the structure in different languages. Every problem comes with a step-by-step algorithm, a walkthrough and time and space complexity. Solutions are given in Python, Java, C++, JavaScript, Go and C#.

Why a fixed list of 75 works

Coverage matters more than count. Two hundred problems drawn from four favourite topics leave you exposed; 75 problems spread over 18 areas do not. A finite list also fits inside a real preparation window, which means you actually finish it, and finishing is what builds confidence.

For deeper work on a single topic, the library's dedicated courses on dynamic programming, graphs, trees and recursion take each area further.

How long it really takes

The stated 25 hours is reading and solving time for someone who already knows basic data structures. Most people should plan three to five weeks at an hour or two a day, because the useful part is attempting each problem before reading the walkthrough, and that takes longer than reading.

Before you start

You should be comfortable in one programming language and know what arrays, hash maps, linked lists, stacks, queues and trees are. The course is labelled beginner level, but it is beginner in interview terms, not programming terms.

Price and ratings

As of September 2026 the course page lists a one-time price of $99 for lifetime access with a certificate, and it is also included in the provider's all-courses subscription. The page shows a 4.7 rating from about 3,500 ratings. Some problems can be tried for free before buying.

How to use it well

• First pass: one topic at a time, attempt each problem for 20 to 30 minutes before opening the solution.
• Second pass, a week later: redo every problem with solutions hidden. The ones you fail are your real revision list.
• Speak while solving. State the approach and complexity out loud, as you would in an interview.

What you can do afterwards

By the end you will have solved a balanced set of 75 representative questions across every major topic, with a personal list of the ones that still need work. That is a solid base for a real loop, and a clear signal of which topic deserves a deeper follow-up course from the same library.

Best for: a focused four to six week sprint before a scheduled coding interview, for candidates who want explanations bundled with the problems.