How to solve LeetCode problems as a beginner?

As a beginner, solving LeetCode problems can feel overwhelming at first, but with the right approach and consistent practice, you’ll gradually build confidence and improve your problem-solving skills. Here’s a step-by-step guide on how to approach LeetCode as a beginner:

1. Start with Basic Concepts

Before diving into solving problems, ensure that you have a solid understanding of basic programming concepts and data structures. Some key concepts you should be familiar with are:

• Variables, Loops, and Conditionals: Basics of how to control flow in your code.
• Functions: Understand how to create and use functions to organize your code.
• Arrays: Learn how to store and manipulate collections of data.
• Strings: Practice working with text data and string manipulations.
• Linked Lists: Understand how linked lists work and how to traverse them.
• Recursion: Understand the concept of functions calling themselves.

If you’re unsure about these topics, spend some time on coding platforms or courses like freeCodeCamp, Codecademy, or YouTube tutorials before jumping into LeetCode.

2. Select Problems Based on Difficulty Level

Start with Easy LeetCode problems to build your confidence and gradually increase the difficulty level to Medium and Hard problems as you improve.

• Sort by Difficulty: On LeetCode, you can sort problems by Easy, Medium, and Hard. Start with Easy problems, which are simpler and involve basic concepts.
• Target 50-100 Easy Problems: As a beginner, focus on solving at least 50 Easy problems before moving to Medium problems. These will reinforce your understanding of basic data structures and problem-solving approaches.

3. Break Down the Problem

When you encounter a new LeetCode problem, follow this structured approach to break it down:

a. Read the Problem Statement Carefully

• Understand the Input and Output: Make sure you clearly understand what the problem is asking for, what kind of input you’re working with, and what output is expected.
• Identify Constraints: Pay close attention to constraints, as they help you choose the most efficient algorithm. For example, a small input size may allow you to use a brute-force approach, while larger input sizes will require optimization.

b. Think of a Simple Approach

• Brute Force First: As a beginner, it’s okay to start with a brute-force solution. This will help you get the problem working and give you a better understanding of the problem.
• Sketch Out Ideas: Write down the steps needed to solve the problem. For example, if the problem asks for the sum of two numbers in an array, think about how you can iterate through the array and find the solution.

c. Test with Sample Inputs

• Use Sample Test Cases: LeetCode provides sample test cases. Test your initial solution on these inputs to see if it works. If it doesn’t, try to understand why.
• Think About Edge Cases: Consider edge cases like empty inputs, large numbers, or inputs with special conditions. Testing edge cases ensures your solution works in all scenarios.

4. Write and Implement the Solution

a. Start Coding

• Write a basic version of the solution, even if it’s not the most efficient. The goal at this stage is to get a working solution.
• Write Clear Code: As you code, make sure to write clean and readable code. Avoid overcomplicating your solution with unnecessary logic.

b. Debug Your Solution

• If your initial solution doesn’t work, use print statements to check variable values at different stages. This will help you understand what’s going wrong.
• Step-by-Step Debugging: LeetCode’s platform lets you run your code with custom test cases. Use this to test edge cases or corner cases you think might break your solution.

c. Optimize After

• Once you’ve got a working brute-force solution, think about how to optimize it. Ask yourself:
  • Can you use a better data structure (e.g., hash maps, sets)?
  • Can you reduce the time complexity by avoiding nested loops or using dynamic programming?
• Don’t Worry About Perfection: At the beginner stage, it's more important to understand how to solve problems than to find the perfect solution. Optimizing will come with experience.

5. Learn from Solutions

After solving a problem, review the LeetCode Discuss section or the official solution (if you have LeetCode Premium). This will help you learn different approaches and optimizations.

• Compare Your Solution: After solving a problem, compare your solution with others to understand alternative approaches.
• Understand Time and Space Complexity: Learn how to analyze and optimize the time and space complexity of your solution.

6. Focus on Problem-Solving Patterns

As you solve more problems, you’ll start noticing patterns in problem-solving techniques. Here are some common ones:

• Two-pointer Technique: Often used in array and string problems.
• Sliding Window: Useful for problems involving subarrays or substrings.
• Recursion and Backtracking: Important for solving problems that require exploring all possible solutions.
• Dynamic Programming: Solving optimization problems by breaking them into smaller subproblems.
• Depth-First Search (DFS) and Breadth-First Search (BFS): For tree and graph traversal problems.

Grokking the Coding Interview by DesignGurus is an excellent resource for learning common coding patterns. You can check it out here.

7. Consistent Practice is Key

• Solve a Few Problems Daily: Aim to solve 1-3 problems per day, focusing on different topics and difficulty levels. This helps you improve steadily.
• Track Your Progress: Keep track of the problems you’ve solved and revisit problems you found challenging after some time.

8. Use LeetCode Discuss and Tutorials

If you get stuck, the LeetCode Discuss section can be helpful:

• Search for Solutions: Many users share detailed solutions, and you can learn different approaches from the community.
• Ask Questions: If you don’t understand a problem or a solution, ask the community for help. Learning from others is an essential part of the process.

9. Use Other Resources if Necessary

If a particular topic or problem type is challenging, supplement your learning with other resources:

• YouTube Channels: Channels like NeetCode, Kevin Naughton Jr., and Clément Mihailescu offer step-by-step solutions to LeetCode problems.
• Courses: Consider taking a course that teaches algorithms and data structures, such as Grokking Data Structures & Algorithms for Coding Interviews by DesignGurus. You can find it here.

10. Stay Patient and Persistent

LeetCode can be challenging, especially as a beginner. The key is to stay consistent, practice regularly, and learn from each problem you solve. It’s okay to get stuck—over time, you’ll develop the problem-solving skills you need to tackle more complex challenges.

Conclusion

To solve LeetCode problems as a beginner:

• Start by mastering basic concepts and Easy problems.
• Break down problems into smaller steps, and don’t rush the coding process.
• Learn from the Discuss section and official solutions to improve your approach.
• Focus on problem-solving patterns and practice consistently to see improvement over time.

With patience and practice, you’ll build the skills you need to tackle more difficult problems and succeed in technical interviews.