By Yumeng Zhang
LeetCode has swiftly become the go-to platform for honing coding skills and preparing for technical interviews. With over 2500 problems, it can certainly seem overwhelming at first. This article is tailored to guide you through this vast array of challenges methodically. Our aim isn't just to help you crack interviews at top tech companies but to cultivate your algorithmic problem-solving skills that stand as invaluable assets in the job market. Here’s a step-by-step guide to mastering LeetCode:
General Principles
Consistency Over Intensity: Pacing yourself is vital. Consistent daily practice is more fruitful than cramming all at once.
Engage Actively: If you find yourself on auto-pilot, take a break. Return with full focus.
Six-Steps Strategy
The strategy is broken down into six steps to help you build a strong foundation in coding interview skills as quickly as possible. If you are one of those guys intimidated by the sheer number of questions and unconfident of pulling this off yourself, keep reading, and you will walk away with a clear game plan.
1. Start with the Top Liked Questions
While LeetCode is a pretty great platform, not all problems are created equal. When you open a problem, you can see how many people upvoted or downvoted a problem. A problem is upvoted if the community finds it clear, helpful, and practical. On the other hand, a problem is heavily downvoted if it’s unclear or unrelated to the general concept of data structures and algorithms. You are recommended to avoid those types of problems in the early stage because your initial focus should be on learning how to play the game instead of battling a boss. So, you can first stay away from problems that have a worse than 2:1 ratio of upvotes to downvotes. Problems that have a 4:1 ratio or above are usually of fairly high quality. These clear and straightforward questions can help you learn more quickly. Initially, target 50 problems of easy to medium difficulty to get a flavor of the platform. Avoid hard problems for now, learn to play the game first.
2. Focus on the Questions by Topic
Rather than hopping randomly from one problem to another, compartmentalize your efforts by topics. You can choose a topic and start drilling down. As you crack questions from the same topic, you will realize that there is a pattern that you can use to solve most of the problems in the same topic. The more time you spend on random problems, the longer it will take for you to get that pattern. Therefore, solve at least 20 questions until you get that pattern for each topic before moving on. Here’s the recommended list of topics (in the order of the topic’s importance, relevance, and frequency) to get you started:
String
Two Pointers
Sliding Window
Binary Search
Recursion
Binary Tree
Backtracking
DFS
BFS
Graph
Linked List
Sort
Trie
Stack/ Queue
Priority Queue
Dynamic Programming
You can also consider beginning with LeetCode 75. This must-do problem list features 75 essential questions, covering a range of topics. It's ideal for beginners to practice and familiarize yourself with trending challenges.
3. Order the Questions from the Highest to the Lowest Acceptance Rate
While LeetCode categorizes problems as easy, medium, or hard, these labels can sometimes be inaccurate. Some mediums can be easier than easies and some easies can be harder than mediums. You would find that the acceptance rate of some easies is lower than 50%, while that of some mediums is higher than even 90%. So do not just blindly attempt easies. A better yardstick is the community-driven acceptance rate. If many LeetCoders found a question easier, you would find it easier too.
4. Learn from the Solutions
Encountering roadblocks is natural. It's possible that it requires an algorithm or data structure that you haven't seen before, and there's no need for you to pull your hair out trying to re-discover an algorithm or data structure. Instead of getting frustrated, focus on understanding the process. If you're stuck for over 45 minutes, it is absolutely fine and more efficient to give up on some problems and check the solution. LeetCode’s “Editorials” section is a great starting point that tends to be fairly high-quality and often includes a well-written code solution. The “Discuss” tab also offers other users’ solutions and strategies that can often provide fresh insights. The key is not just to find the solution but to genuinely understand it. If you grind the problems by learning some solutions from the experts, you will start to see the pattern and develop the technique needed to solve other similar questions.
5. Revisit the Problems
Once you understand a problem, revisit it periodically. This ensures that your understanding is deep-rooted. It’s not just about solving it once but being able to consistently apply the learned logic.
6. Solve Company-Specific Questions
As you advance, you might have specific dream companies. LeetCode premium can filter problems based on company preferences. You can even sort them by their frequency in a selected time period. There is no guarantee that these problems will show up in your interview but the list is pretty accurate. It’s a great tool but use it judiciously. The endgame is to develop skills, not just memorize a set of problems.
Wrapping Up
LeetCode, with its multitude of challenges, offers a platform for continuous growth. It's not about the number of problems solved but the depth of understanding achieved. With a structured approach, commitment, and a focus on learning, you're not just preparing for interviews—you're gearing up for a successful career in tech. Embrace the process and let LeetCode be your companion in this journey.