LeetCode Methodology
LeetCode is hard. Once, I tried to work out problems on my own without looking at the solutions. It was a laborious and frustrating journey. I could only work on at most one or two problems a day. Often, after many hours of head-scratching, my solution turned out wrong in the end. When I returned to the same problem after a few days, I would still forget how to solve it.
Recently, I came across this advice and found it particularly helpful.
Original Twitter thread:
The way i prepared for coding interviews before i got my job at Facebook is a bit different from what most people suggest. I never forced myself to solve problems without using google. I would google the answer after i was stuck even for 1 minute
— Aaron Abramov (@aarondjents) May 28, 2020
Text version (with typo fixed):
The way I prepared for coding interviews before I got my job at Facebook is a bit different from what most people suggest. I never forced myself to solve problems without using google. I would google the answer after I was stuck even for 1 minute If I tried to solve it myself I’d easily spend 2-3 hours on one question and that seemed like a waste of time.
My process involved saving a bunch of interview questions in a folder and going through them as fast as possible. Don’t know how the answer right away? No problem, Google the solution and code it out (no copypasta tho).
This way I was able to go through a lot of questions every day. Twenty, maybe thirty per day. After 100 or so, I would delete all my solution and go through the same list again. Most solution I already remembered, some of them I forgot and had to Google again. I would go through the same list again and again until I can solve 100% of those question without using google. This way, instead of wasting time on staring at the question and trying to find the solution yourself I coded a lot. What I found is that after 200-300 questions most of them start repeating themselves in different shape. The question might be different, but underlying problem is the same array sorting or tree traversal.
Eventually it got to the point where I couldn’t find any questions that would surprise me. Every new question was “the same sorting but numbers are negative” or “instead of packing the backpack we’re counting coins”.
Coding a lot also makes you more familiar with the programming language you chose. It becomes almost like a native language. You don’t spend minutes trying to figure out how to write that “for” loop. You just write it.
Aaron Abramov
J. Li also gives similar advice in his blog post How I leetcode for 6 months and land a job in FANG.
I feel doing LeetCode is a lot like doing math, which boils down to pattern matching on what you have already learned and memorized. It simply takes a lot of practice and repetition.
Also, based on my own experience, LeetCode’s easy-medium-hard classification refers to the complexity of the code, not necessarily how difficult it actually is to solve it on your own. This is especially true for dynamic programming problems like this one.
I wrote about this problem in this post. It has an interactive table that shows how the numbers are calculated. Once you know the algorithm, the code is not difficult to write. But the algorithm itself is not easy to think up at all. So don’t be frustrated when you feel you can’t even solve some “easy” problems.