Ketan Khairnar ketankhairnar

Basics

B-trees and CPU Caches

GROKKING NOTES

I liked the way Grokking the coding interview organized problems into learnable patterns. However, the course is expensive and the majority of the time the problems are copy-pasted from leetcode. As the explanations on leetcode are usually just as good, the course really boils down to being a glorified curated list of leetcode problems.

So below I made a list of leetcode problems that are as close to grokking problems as possible.

Pattern: Sliding Window

Quick Tips for Fast Code on the JVM

I was talking to a coworker recently about general techniques that almost always form the core of any effort to write very fast, down-to-the-metal hot path code on the JVM, and they pointed out that there really isn't a particularly good place to go for this information. It occurred to me that, really, I had more or less picked up all of it by word of mouth and experience, and there just aren't any good reference sources on the topic. So… here's my word of mouth.

This is by no means a comprehensive gist. It's also important to understand that the techniques that I outline in here are not 100% absolute either. Performance on the JVM is an incredibly complicated subject, and while there are rules that almost always hold true, the "almost" remains very salient. Also, for many or even most applications, there will be other techniques that I'm not mentioning which will have a greater impact. JMH, Java Flight Recorder, and a good profiler are your very best friend! Mea

Code is clean if it can be understood easily – by everyone on the team. Clean code can be read and enhanced by a developer other than its original author. With understandability comes readability, changeability, extensibility and maintainability.

General rules

Follow standard conventions.
Keep it simple stupid. Simpler is always better. Reduce complexity as much as possible.
Boy scout rule. Leave the campground cleaner than you found it.
Always find root cause. Always look for the root cause of a problem.

Design rules

List AWS regions and parsing using jq:

$ aws ec2 describe-regions | jq '.Regions[].RegionName'

"ap-south-1"
"eu-west-1"
"ap-southeast-1"
"ap-southeast-2"
"eu-central-1"
"ap-northeast-2"

Applied Functional Programming with Scala - Notes

1. Mastering Functions

A function is a mapping from one set, called a domain, to another set, called the codomain. A function associates every element in the domain with exactly one element in the codomain. In Scala, both domain and codomain are types.

val square : Int => Int = x => x * x

	import java.util.*;

	@SuppressWarnings("ALL")
	class Test {
	static class ReifiedList<T> extends AbstractList<T> {
	private final List<T> delegate = new ArrayList<>();
	private final Class<?> type;

	@SafeVarargs
	ReifiedList(@Deprecated T... unused) {

	1、select avg(ss_item_sk) from store_sales;
	2、select ss_sold_Date_sk,count(*) as cnt from store_sales group by ss_sold_Date_sk order by cnt desc,ss_sold_Date_sk limit 10;
	3、select ss_sold_Date_sk,avg(ss_item_sk) as cnt from store_sales group by ss_sold_Date_sk order by cnt desc,ss_sold_Date_sk limit 10;
	4、select ss_item_sk,count() from store_sales group by ss_item_sk having count()>1 limit 10;
	5、select sum(ss_item_sk) from store_sales;
	6、select ss_sold_Date_sk,ss_wholesale_cost,avg(ss_item_sk) as cnt from store_sales group by ss_sold_Date_sk,ss_wholesale_cost order by cnt desc,ss_sold_Date_sk limit 10;
	7、select ss_sold_Date_sk,ss_wholesale_cost,avg(ss_item_sk) as cnt from store_sales group by ss_sold_Date_sk,ss_wholesale_cost order by cnt desc,ss_sold_Date_sk limit 10;

	8、select ss_sold_Date_sk,ss_wholesale_cost,avg(ss_item_sk) as cnt,count(distinct(ss_sales_price)) as avg1 from store_sales group by ss_sold_Date_sk,ss_wholesale_cost order by cnt desc,ss_sold_Date_sk limit 10;

	import org.slf4j.Logger;
	import org.slf4j.LoggerFactory;

	import java.io.IOException;
	import java.nio.file.*;

	public class FileWatcher {
	private static final Logger log = LoggerFactory.getLogger(FileWatcher.class);

	private Thread thread;

	Just do something, doesn't matters what
	Book == blog archives. Feel free to scram
	We are creatures of habits (but don't condition habits with identity/ego). Have deliberate habits
	Stopping alcohol
	Unpack causes
	- availability
	- desire

	Availability => Early morning sport. Force to not go out at night too much.
	Desire