## Introduction to Sequelize ORM

This is about the basic usage of Sequelize ORM – how to create migrations, models, seeders and how to get the data from the database. Everything is explained on an example project, which you can find on GitHub.

## Lexicographical permutations

The solution for Bigger is Greater challenge on HackerRank, or how to generate next lexicographically greater string. Problem description, algorithm steps and complete source code to solve this challenge.

## Google Code Jam 2017: Oversized Pancake Flipper

Last year, the Infinite House of Pancakes introduced a new kind of pancake. It has a happy face made of chocolate chips on one side (the “happy side”), and nothing on the other side (the “blank side”).

You are the head cook on duty. The pancakes are cooked in a single row over a hot surface. As part of its infinite efforts to maximize efficiency, the House has recently given you an oversized pancake flipper that flips exactly K consecutive pancakes. That is, in that range of K pancakes, it changes every happy-side pancake to a blank-side pancake, and vice versa; it does not change the left-to-right order of those pancakes.

You cannot flip fewer than K pancakes at a time with the flipper, even at the ends of the row (since there are raised borders on both sides of the cooking surface). For example, you can flip the first K pancakes, but not the first K – 1 pancakes.

Your apprentice cook, who is still learning the job, just used the old-fashioned single-pancake flipper to flip some individual pancakes and then ran to the restroom with it, right before the time when customers come to visit the kitchen. You only have the oversized pancake flipper left, and you need to use it quickly to leave all the cooking pancakes happy side up, so that the customers leave feeling happy with their visit.

Given the current state of the pancakes, calculate the minimum number of uses of the oversized pancake flipper needed to leave all pancakes happy side up, or state that there is no way to do it.

## Prime numbers

With this post I want to begin a series of posts about general algorithms. It is not an accident I started with the prime numbers. This is basic problem to solve when you are starting with programming. And one more reason – I was curious how RSA algorithm works and the important part of the algorithm is to generate two random big prime numbers.

I am working for a Start Up project – DiagramArt, where we needed to create Android application which : load list of diagrams from API, show these diagrams to the user and some other stuff of course. The list consists from a preview picture, diagram’s title and its description. There is no problem to load and show these data, the problem was in the preview picture.

## Where do I take my energy

Few weeks ago in the late night, my friend asked me, where do I take the energy. He knows I have work, couple of sides projects and from time to time I try to write here some post. Is it some kind of a coffee? Or something else? I didn’t know how to answer, but I was thinking about it during a walk.

## Express server with JWT authentication

I needed to create a simple server, that would have one “public” route `/login` and other routes are available only for users with valid JWT token.

That means, the user is allowed to log into the system and then get any data from it. If he is not logged in and he tries to get some data, he only get an error message and 401 ( Unauthorized ) status code will be returned.

## How to send HTTP GET / POST request in Java

This post describes how to make HTTP GET and POST request on server. I will use httpbin server for testing. It returns you everything you send there : query params, post data, headers, etc.