How many LeetCode problems are sufficient?

The number of LeetCode problems you need to solve to feel well-prepared for coding interviews depends on your goals, target companies, and experience level. While there’s no magic number, solving a strategic mix of Easy, Medium, and Hard problems across key topics can prepare you effectively for technical interviews. Let’s break down a general approach to how many problems might be “sufficient” for most people.

1. Number of Problems Based on Experience Level

Beginners (100 to 150 Problems)

• Focus: Learn and solidify core concepts and basic problem-solving skills.
• Problem Breakdown:
  • 60-80 Easy Problems: Start with foundational topics like arrays, strings, hash maps, and basic recursion. Solving a good number of Easy problems helps build your confidence.
  • 30-50 Medium Problems: Once you're comfortable with Easy problems, transition to Medium-level problems. Focus on dynamic programming, trees, graphs, and binary search algorithms.
  • 10-20 Hard Problems: While Hard problems can be intimidating for beginners, attempting a few toward the end of your preparation will help you stretch your problem-solving skills.

Intermediate (200 to 300 Problems)

• Focus: Improve speed, efficiency, and ability to tackle more complex problems.
• Problem Breakdown:
  • 50-70 Easy Problems: Refresh your understanding of basic algorithms and data structures. These problems should feel more like warm-ups by this stage.
  • 100-150 Medium Problems: This is where you should spend most of your time. Medium problems are the backbone of coding interviews and cover the majority of algorithmic challenges.
  • 30-50 Hard Problems: To fully prepare for top-tier companies like FAANG, it's important to tackle harder problems that test your knowledge of advanced concepts (e.g., dynamic programming, advanced graph algorithms).

Advanced (300 to 500+ Problems)

• Focus: Sharpening skills for high-level technical interviews and competitive programming.
• Problem Breakdown:
  • 30-50 Easy Problems: Use Easy problems to refresh basic concepts and improve speed.
  • 150-200 Medium Problems: These should be your bread and butter, as most technical interviews will focus heavily on Medium-difficulty problems.
  • 100-150 Hard Problems: Focus on solving complex problems that require advanced knowledge of algorithms, optimization techniques, and deep problem-solving skills. These are common for interviews at companies like Google, Facebook, and Apple.

2. Problem Categories to Focus On

Regardless of the number of problems you solve, it’s crucial to cover a wide range of topics that are typically tested in coding interviews. Here are the key topics to focus on:

Core Topics:

• Arrays and Strings: Understanding array manipulation, sliding window techniques, and common string operations.
• Linked Lists: Mastery of traversing, reversing, and merging linked lists.
• Binary Search: Learn how to implement binary search for finding elements or solving optimization problems.
• Dynamic Programming: Solve common DP problems such as fibonacci, knapsack, and longest increasing subsequence.
• Trees and Graphs: Focus on tree traversal algorithms (DFS, BFS), binary trees, and common graph problems (shortest path, topological sorting).
• Sorting and Searching Algorithms: Master quicksort, mergesort, and binary search techniques.
• Backtracking: Solve problems that require exploring all possible solutions (e.g., N-Queens, Sudoku Solver).
• Recursion: Understand recursive problem-solving approaches and base cases.

Advanced Topics:

• Heaps and Priority Queues: Focus on problems involving min-heaps and max-heaps.
• Graphs: Dive deeper into graph algorithms like Dijkstra’s, Prim’s, and Floyd-Warshall.
• Bit Manipulation: Practice problems involving bitwise operations (e.g., finding missing numbers, subsets).
• Trie and Advanced Data Structures: Work with tries, segment trees, and Fenwick trees for specific types of problems.

3. Problem Difficulty Breakdown

A good rule of thumb is to distribute your practice across different difficulty levels, with most of your focus on Medium problems since they make up the majority of coding interviews.

• Easy (20-30%): These problems help reinforce foundational knowledge. You should be able to solve them quickly, and they serve as warm-ups before tackling more challenging problems.
• Medium (50-60%): Spend the majority of your practice time here. Medium problems represent the bulk of interview questions and cover a wide range of essential concepts.
• Hard (10-20%): Tackling Hard problems will help you think outside the box and develop advanced problem-solving skills. This is especially important if you're targeting top-tier tech companies or senior positions.

4. Recommended Number of Problems for Specific Goals

1. Preparing for Coding Interviews at FAANG or Similar Companies (250 to 350 Problems)

• These companies typically focus on Medium and Hard problems.
• Solving 150-200 Medium problems and 50-100 Hard problems across various topics will give you the depth needed to tackle their interviews confidently.

2. General Interview Preparation (150 to 200 Problems)

• If you’re preparing for interviews at mid-tier or smaller tech companies, solving 50-60 Easy problems and 100-120 Medium problems will likely be sufficient.
• Focus more on breadth rather than diving too deep into Hard problems unless you’re aiming for highly competitive roles.

3. Competitive Programming or Mastery (500+ Problems)

• For competitive programming, you’ll need to go beyond typical interview prep.
• Solving 200+ Hard problems and working on timed challenges in coding competitions is essential for honing speed and accuracy.

5. Practice Tips for Efficient Preparation

1. Solve a Diverse Range of Problems: Make sure to practice problems from each category (arrays, strings, dynamic programming, graphs, etc.) to ensure you’re well-rounded.
2. Focus on Weak Areas: Identify which topics you struggle with the most and spend extra time improving in those areas.
3. Review Solutions: After solving a problem, review your solution and compare it with others on LeetCode Discuss. This helps you learn different approaches and optimizations.
4. Don’t Memorize: Focus on understanding the logic behind the problems, rather than memorizing solutions. Coding interviews often involve similar patterns but with twists, so understanding the concept is key.
5. Practice Mock Interviews: Use platforms like Pramp or LeetCode Premium’s mock interview feature to simulate real interview conditions.

6. Conclusion

The number of LeetCode problems you need to solve depends on your current experience and the types of companies you’re targeting. Here's a quick summary:

• Beginners: Aim for 100 to 150 problems, focusing on core concepts and easy/medium problems.
• Intermediate: Solve 200 to 300 problems, with most of your practice on medium and hard problems.
• Advanced: Target 300 to 500+ problems, focusing on medium and hard problems to master advanced algorithms and optimization techniques.

Remember, it’s not just about the number of problems but the quality of your practice. Focus on understanding concepts, reviewing solutions, and tackling a wide range of problems across all important topics. Consistency is key—set a daily or weekly goal and stick to it.