cabin

@title: Leetcode, an honest review

@date: 2025-01-01

@language: en

@categories: general, leetcode

# Leetcode an honest review

## Overview

My [leetcode journey](https://leetcode.com/u/dimitrijed/) has started on Nov 5, 2022 as a way to prepare for

algorithms class. As I've done more and more problems it slowly turned into an

obsession. I was doing problem after problem, from many different categories.

For the duration of 2023 and 2024, every single day, I've been doing at least

one problem - a Daily problem if it hasn't already been solved, or a random

problem if it has. Usually, that was all I did, but when I was bored, I

would do 5, 10 or even 20 problems.

The summary is as follows (at the time of writing):

* Streak: 737/789 days

* Rank: 3,601/~5mil people

* Easy: 350/846 problems

* Medium: 968/1775 problems

* Hard: 182/785 problems

* Total: 1500 problems

* Badges: 44

## Routine

During the day, when I found the time, I sat down ready to tackle one

problem. I would do my best to solve it without looking at hints and solutions.

Goal was to find the best possible algorithm, which in practice means beating

85% submissions or more. Based on the problem, this would take anywhere between

5 and 20 minutes, and then I would try to utilize a hint, in case there was

something I'd missed.

If that didn't help, I would turn to the official or community solution, in

order to understand what I'd missed and how exactly does the algorithm need to

work, then I would try to implement it myself, often more clearly and

concisely. Even if I've managed to solve a problem in the satisfactory

complexity, I would still take a look at the solutions just to see whether

there is something worth remembering. I've picked up a lot of great trick

this way.

## Learning

Because of my competitive programming background from middle school and high

school, I was already quite familiar with the format as well as logical

thinking, which has kick-started the beginning.

At that time, I've been writing a lot of C, but I wanted to get good at C++.

I'd seen STL before, but I lacked deep understanding of it all. I've started

with some introductory problems, that mostly tested logic, but soon enough I

started dabbling with more advanced topics like Trees and Graphs. That is where

the real fun began. I was aware of the few algorithms from the class, but when

it came time to actually implement them I was thunder struck. It was a crucial

step at the time to take a look at other people's solutions and see how exactly

are the data structures represented in C++ code, and how to interact with them.

As my knowledge of algorithms grew, so did my understanding of C++, although

I've spent an additional time learning about it's inner workings. It came to

the point where language was not an issue anymore. That's when I've started

thinking beyond the problem at hand, and more about the codding style, as

well as the best utilization of processor and memory.

## Problems

There are many different kinds of problems, regardless of their difficulty:

* Brain testers - usually math related and require logical thinking

* Strictly math problems - based on advanced math knowledge

* Little problems - not necessarily hard, but can be tricky to implement elegantly

* Straight foreword problems - one you've seen the underlying idea, they are

not that difficult

* Problems that require a well-known algorithm in order to be solved. I don't

think any mortal can come up with them in any reasonable amount of time.

Most of the problems require a specific technique to be solved, such as sliding

window, two pointer, binary search... The more problems you do, the easier it

will be to spot these patterns quickly, and implement the adequate solution.

The issue may arise, when a few of these techniques are required simultaneously.

## Difficulty.

Easy problems are easy mainly because of the restrictions. Any valid solution,

regardless of the complexity, will work. Most of them are trivial, but there

are a few hidden gems that serve as an introduction to a well-known algorithms

to be used in harder problems. This is a good reason to look at other solutions

even if running time is satisfactory - inefficiency is masked by small constants.

Medium problems vary drastically. There are some trivial ones, some that are

just tedious to code, some that require solid understanding of common

algorithms and data structures, while some require specific algorithm that is

worth remembering. Due to the wide array of possibilities, there are some

medium problems that I've solved in under a minute, while even after I've done

so many of them, from time to time, I come across one that I have no idea where

to even start. This is a fact of life, and there is no point in beating your

head about it.

Hard problems are weird. There are some that require ultra specific algorithms,

some that require outstanding out the box thinking, while still being possible

to come up with. My favorite ones are those that require perfect

understanding of the common algorithms and data structures, then adding some

twist to it, whether it's a combination or transformation that is needed in

order for it to work. Some are just impossible to understand, even with a

solution...

## Advice

Doing 1500 problems is really unnecessary if your main focus are interviews.

Focusing on [neetcode](https://neetcode.io/) will be enough for most people.

There are a few things worth remembering:

* Code, Code, Code! Every single solution needs to be actually coded,

tested and run. There are no too easy problems. Everything counts.

* You need to be aware of your weaknesses, whether it's the understanding

of the language that is holding you back, or it's some algorithm or a

data structure.

* Once you've learned a new concept, you should drill it until it becomes

second nature. There should be no rush between problems, unless everything

is crystal clear. Otherwise you will waste a lot of time reviewing concepts

that should have been mastered a long time ago.

* Not everything is in the algorithms and data structures. Clean and concise

code also matters a lot

* Copying the solution to the paper by hand really helps internalize the ideas.

Do this only for a small number of special problems, as not to waste too much

time.

## Conclusion

I'll be taking a break, possibly forever, form leetcode. It's been fun, but

I've passed the point of diminishing returns for where I want to be, so it's

better for me to focus my energy elsewhere. The lesions I've learned will

continue to serve me in the future, both the algorithms and data structures, as

well as the logic and general practice of coding.

I haven't given competitions an honest shot, mostly due to the incontinent time

at which they are held. Although, they might be a new step forward, to keep me

from getting rusty.