How much LeetCode is enough for Google?

Preparing for a technical interview at Google is a rigorous process, and solving LeetCode problems is a great way to practice for the coding portion of the interview. However, there’s no fixed number of problems that guarantees success. Instead, focusing on consistent practice, understanding problem-solving patterns, and mastering key algorithms and data structures is crucial.

Here’s a guide to how many LeetCode problems you should aim to solve to feel well-prepared for a Google interview.

1. Recommended Number of LeetCode Problems

For Beginners (150-200 Problems)

• Goal: Build a strong foundation in algorithms and data structures.
• Problem Breakdown:
  • 50-70 Easy Problems: Focus on mastering basic data structures like arrays, strings, linked lists, and hash maps. Solving these problems helps build your confidence.
  • 80-100 Medium Problems: Once you're comfortable with Easy problems, spend most of your time on Medium problems, as they make up the bulk of Google’s interview questions. Practice dynamic programming, recursion, and tree/graph algorithms.
  • 20-30 Hard Problems: As you get closer to the interview, attempt some Hard problems. Google interviews may include complex problems that require advanced knowledge of dynamic programming, graph theory, or backtracking.

For Intermediate Candidates (200-300 Problems)

• Goal: Sharpen problem-solving speed and efficiency.
• Problem Breakdown:
  • 30-50 Easy Problems: Use Easy problems as warm-ups or to review fundamental concepts.
  • 120-150 Medium Problems: Focus on solving Medium problems across a wide range of topics, such as binary trees, graphs, dynamic programming, and sliding window techniques. These are the types of problems you’re most likely to encounter at Google.
  • 40-60 Hard Problems: Google interviewers sometimes ask challenging problems that require creative approaches, so make sure to practice Hard problems. These problems will improve your ability to think outside the box and optimize solutions.

For Advanced Candidates (300-500+ Problems)

• Goal: Master advanced problem-solving techniques and optimization.
• Problem Breakdown:
  • 30-50 Easy Problems: Use these as quick refreshers and warm-ups.
  • 150-200 Medium Problems: Spend most of your practice time on Medium problems, as this is the core difficulty level in Google interviews. Focus on topics like dynamic programming, recursion, and graph traversal (DFS, BFS).
  • 100+ Hard Problems: Advanced candidates should spend a good amount of time solving Hard problems to master advanced concepts and build problem-solving stamina. Google interviews at the senior level often include these more complex problems.

2. Key Problem Categories to Focus On

To maximize your preparation for Google interviews, it’s important to cover key topics that are commonly asked in their technical interviews. Here's a list of topics and problem types to focus on:

• Arrays and Strings: Master the fundamentals of array manipulation, sliding window techniques, and string operations.
• Linked Lists: Focus on traversal, reversing linked lists, detecting cycles, and merging sorted lists.
• Binary Search: Learn how to apply binary search to both standard and tricky problems.
• Trees and Graphs: Spend significant time on binary trees, DFS, BFS, and graph problems like topological sorting and shortest paths.
• Dynamic Programming (DP): Master DP concepts such as memoization, tabulation, and common DP problems like longest increasing subsequence and knapsack.
• Recursion and Backtracking: Practice solving problems that require recursive approaches, including N-Queens and Sudoku Solver.
• Sorting and Searching Algorithms: Understand sorting techniques and how to optimize search algorithms using binary search or other techniques.
• Hash Maps and Heaps: Problems that require fast lookups and priority queues are commonly tested.
• Greedy Algorithms: Google interviews often include problems that require you to find optimal solutions using greedy methods.

3. What’s More Important Than the Number of Problems?

While solving a sufficient number of problems is important, other aspects of your preparation can significantly impact your success:

a. Problem-Solving Patterns

• Recognize Patterns: Many LeetCode problems follow common patterns, such as sliding windows, two-pointer techniques, and dynamic programming structures. Focus on recognizing these patterns, as this will help you solve problems faster.
• Optimize Solutions: Focus on writing clean, efficient code. Google values solutions that are optimized for time and space complexity, so after solving a problem, always try to refactor and improve your solution.

b. Understanding vs. Memorization

• Understand the Logic: Instead of memorizing solutions, focus on understanding the underlying logic. Google interviewers will often present variations of common problems, and if you truly understand the problem, you’ll be able to adapt to these variations.

c. Mock Interviews and Timed Practice

• Mock Interviews: Practice with mock interviews to simulate real interview conditions. This will help you manage time pressure and improve your ability to articulate your thought process.
• Timed Practice: In real interviews, you have a limited amount of time to solve problems, so practicing under time constraints is essential. Try to complete Medium problems in 30-40 minutes and Hard problems in 60-90 minutes.

4. Additional Resources for Google Interview Prep

• LeetCode Premium: Consider investing in LeetCode Premium to get access to company-specific problem sets that are frequently asked in Google interviews.
• DesignGurus Courses:
  • Grokking the Coding Interview: Patterns for Coding Questions: This course is great for learning common patterns used to solve coding problems.
  • Grokking Data Structures & Algorithms for Coding Interviews: Useful for mastering key data structures and algorithms.
• Mock Interviews:
  • Use platforms like Pramp or LeetCode Premium's mock interview feature to simulate interviews and receive feedback.

5. Conclusion

To prepare for a Google interview, solving 200 to 300 LeetCode problems is a reasonable target for most candidates. You should focus on Medium problems since they make up the bulk of Google’s interview questions. Here’s a quick recap:

• Beginners: Solve 150 to 200 problems, focusing on Easy and Medium problems.
• Intermediate: Solve 200 to 300 problems, with most of your time spent on Medium problems.
• Advanced: Aim for 300 to 500+ problems, focusing on Medium and Hard problems.

Remember, consistency is key, and the quality of practice (understanding patterns and solving problems efficiently) is just as important as the quantity of problems solved.