DEV Community: nicha

[Neetcode] When to buy and sell stock

nicha — Thu, 24 Jul 2025 09:53:06 +0000

This is my first article in the Neetcode practice series. In this series, I'll be jotting down my approach to problems and how I pick up better habits along the way.

So, let's dive in!

This problem is here:
https://neetcode.io/problems/buy-and-sell-crypto?list=blind75

Essentially, the goal is to determine the lowest price to buy a stock and the highest price to sell it at to maximise profit.

Bruteforce

The most straightforward way to tackle this is to loop through every possible "buy" price, then check every "sell" price after it, calculating the profit each time to find the maximum.

class Solution:
    def maxProfit(self, prices: List[int]) -> int:
        max_profit = 0
        for index, p in enumerate(prices):
            for j in range(index+1, len(prices)):
                profit = prices[j] - p
                if profit > max_profit:
                    max_profit = profit 

        return max_profit

The outer loop picks a buy price. The inner loop then scans all the prices after the buy price to find a sell price. We calculate the profit for each pair and update max_profit if a better one is found.

This setup involves a nested for loop, resulting in a time complexity of O(n^2) – not ideal for large lists.

A Better Approach

If I step back and think about it, we only need to go through the prices once. We can keep track of the lowest buy price we've seen so far and, as we iterate, continually update our max_profit with the current sell price minus that lowest buy price. If we encounter a price lower than our current buy, that becomes our new buy price, because it opens up the possibility of even greater future profits.

class Solution:
    def maxProfit(self, prices: List[int]) -> int:
        max_profit = 0
        buy = prices[0]
        for sell_price in prices:
            max_profit = max(max_profit, sell_price-buy)

            # If the current 'sell_price' is lower than our 'buy' price,
            # it means we found a new, better (lower) potential buy point.
            # So, we update our 'buy' price.
            buy = min(buy, sell_price)
        return max_profit

In this code, we start to buy from the very first price. As we loop through prices (treating each sell_price as a potential sell point):

We calculate the profit we'd make if we bought at our buy price and sold at the sell price.
We update max_profit to be the higher of its current value or current profit.
Crucially, we then check if sell_price is lower than our current buy price. If it is, then the sell_price becomes our new buy price, because buying at that point would give us a better starting position for future profits.

This single loop means our time complexity is significantly more efficient, at O(N).

If you're on the same journey of practising LeetCode, let's do this together!

For a bit of extra motivation, I want to share some wise words from the author of this Anki deck: https://ankiweb.net/shared/info/1941530701

Getting good at DSA is not about having a strong intuition or being good at puzzle solving. If I ask you some dumb math like 2+2, you instantly know the answer is 4. This is because you have spent years and years using and testing your basic arithmetic skills. If you ask a 2 year old what 2 + 2 is, they'll likely tell you their favorite color is yellow. The 2 year old is not dumb, they just don't have enough exposure to arithmetic concepts yet. Learning DSA is similar.

If it takes you 1 hour to solve an easy, it doesn't mean you're stupid. It means you're wasting your time. Limit how much time you spend with each problem to maximum 5 minutes, before looking at the answer. Then use spaced repetition to revisit problems you've already learned how to solved in the future. If you limit the amount of time you spend on each problem, you will solve 10 times more problems an hour. You will have exposure to all the tools you need to solve almost any problem on leetcode in a month. You will be able to solve most new problems in less than 5 minutes, which gives you plenty of time to solve similar problems in a room full of strangers for 4 hours straight.

We got this! Until we meet again, Happy coding :)

[Discord] Send message through Bot

nicha — Thu, 10 Aug 2023 14:57:58 +0000

I am a newbie to Discord. Recently, my friend and I started a discord channel for a live talk session to interview people and share our experiences with interested people.

When sending a message, I'm thinking about a way to send a message through a bot instead of using my account, so my friend taught me a way to do that. And today, you will know it too!!

First of all, you have to be an admin of that server. Then, visit the server setting > integration > webhook.

Then, click "New Webhook" and choose the channel that you want to send message to

Later on, click on the button "Copy Webhook URL" to copy the webhook URL

Lastly, you can send a message by inputting it into the curl.

curl --location --request POST '{YOUR_WEBHOOK_URL}' \
--header 'Content-Type: application/json' \
--data-raw '{
    "content": "{YOUR_MESSAGE}",
    "username": "{SENDER_NAME}",
    "avatar_url": "{PICTURE_URL}"
}
'

Please feel free to share interesting bot and command in discord with me 👾

50th Percentile is Median NOT mean

nicha — Wed, 19 Oct 2022 15:45:26 +0000

I was confused whether 50th Percentile is Mean or Median. So, I will noted down right here that it is MEDIAN

Imagine that there are 9 people in a room. Some are children, teenagers, and adults

These are their age sort in ascending.

5, 10, 15, 20, 25, 30, 35, 40, 45

From the dataset above:
Median = 25
Mean = 25

Calculate median:
Median position = (n+1)/2 
with n = 9 the median position is 5, which is 25

Calculate mean:
(5+10+15+20+25+30+35+40+45)/9 = 25

In this case, the mean and median is equal due to the age is symmetrically distributed

On the other hand, if the people in the room is mostly young, those young kids will make the group look younger.

Although the middle person is 20, the majority is so young that the mean goes down.

1,2,3,4,5,20,21,22,30

Median = 20
Mean = 12

And when majority of the group is older, the mean will rise and become higher

18,19,23,30,43,60,65,70,90

Median = 43
Mean = 46.44

Reference:

Does 50th Percentile mean Average?

Encoding, Encryption, Hash

nicha — Tue, 26 Apr 2022 12:43:50 +0000

Encoding
Use to change the format of the code to different format for usability. The encoding technique is public, so any one who know how to read can get the information.
Encryption
Use for security purpose. We can encrypt the data using key to make it unreadable by people who don't have the key. If we want to read the data, we need to decrypt it using the key.
Hash
Use to check the integrity of the data. By hashing the same data, it will always yield the same result. However, we cannot transform the hash data back to the original one.

Go Doc

nicha — Sun, 09 May 2021 10:46:30 +0000

Go help developers generate documents by using godoc

Reference: https://golang.org/doc/effective_go

Generating godoc is fairly easy. The developer just put the comment on top of the file before the package clause, then the doc will be generated automatically.

There are two types of comment - block comment, and line comment

1.Block comment /* */ use for several lines of comment

/*
Package regexp implements a simple library for regular expressions.

The syntax of the regular expressions accepted is:

    regexp:
        concatenation { '|' concatenation }
    concatenation:
        { closure }
    closure:
        term [ '*' | '+' | '?' ]
    term:
        '^'
        '$'
        '.'
        character
        '[' [ '^' ] character-ranges ']'
        '(' regexp ')'
*/
package regexp

2.Line comment // use for a simple comment

// Package path implements utility routines for
// manipulating slash-separated filename paths.

For multi-file packages, the package comment only needs to be present in one file.

What should be in the comment?

Package introduction
Package explanation as a whole

Other than that you could comment on top of functions, interfaces or type, etc. to add further explanation

How to see godoc locally

A. cd into the package then run

go doc

This will show the doc in the terminal

B. If you want to see it on the local web

1.Make sure you have the go.mod file in the root directory
if you don't have it yet run

go mod init example/path

2.run

godoc

then it will run on localhost:6060

if you want to, you can specify your own port

godoc -http=localhost:8080

Week1: NPM & Package-lock.json

nicha — Fri, 23 Apr 2021 02:10:37 +0000

How to install npm

When you install nodejs you will get npm along with it
https://nodejs.org/en/download/

To check node and npm version

node -v
npm -v

NPM stands for Node Package Manager

it is a package manager for Javascript

The uses of npm are

It is an online repository for the publishing of open-source Node.js projects

FOR EXAMPLE:
if you want to import the testing framework you can just install it by

npm install --save-dev jest

It is a command-line utility for package installation, version management, and dependency management.

FOR EXAMPLE:
if you have module @jest/core, you can update to the latest version by

npm install @jest/core@latest

Once you install the library, it will store in node_modules

Normally, node_modules gonna be a big folder, so you do not push it into git.

It is recommended to have package.json and package-lock.json, to help you know those libraries and their versions

To create a package.json file

npm init

Package.json - list the version of its dependencies (library we install), and also other project information such as name, version, author, script, etc.

Package-lock.json - list solely about the dependencies in depth

Now when you want to install those libraries, npm can get the info from package-lock.json

To install dependencies just run:

npm install

Also keep in mind that:

You can have only package.json
But you can not have only package-lock.json file

package-lock.json have to come with package.json

** And both files need to be stored in git

Reference:
https://nodejs.org/en/knowledge/getting-started/npm/what-is-npm/
https://stackoverflow.com/questions/45052520/do-i-need-both-package-lock-json-and-package-json#:~:text=No.-,The%20package.,to%20a%20specific%20version%20number.

WEEK1: GIT Conventional Commit

nicha — Thu, 22 Apr 2021 15:03:58 +0000

This will provide a set of rule to make your commit easier to read
https://www.conventionalcommits.org/en/v1.0.0/
https://gist.github.com/qoomon/5dfcdf8eec66a051ecd85625518cfd13

To summarize:

feat - use when a new feature is added
fix - fix a bug
refactor - rewrite/restructure code (no behavior changes)
perf - improve performance
style - style of the file eg. white spaces, formatting, semicolon
test - add test or update test
docs - format the document not code
build - build component eg. project version, dependencies
ops - infrastructure
chore - other miscellaneous commits eg. update .gitignore

NOTE:

Use present tense
Don't capitalize the first letter
No dot at the end

Example

docs: correct spelling of CHANGELOG

Can also add scope like this

feat(lang): add polish language

WEEK 0: Create Vue3

nicha — Sun, 18 Apr 2021 04:37:43 +0000

Create folder frontend and get inside

mkdir frontend
cd frontend

Create new vue project

vue create to-do-list

WEEK 0: First Commit

nicha — Sat, 17 Apr 2021 13:54:32 +0000

Welcome to my first blog :)

From now on I would like to commit to writing a post at least once a week.

These are topics I would like to start study with.

Docker
Vue3
Golang
Kafka
RabbitMQ

I will try to sum up what I study each week, and let see how much I could learn in a year.