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How to find a random permutation of the sequence 1, 2,..., 15 that can be used as the initial state of the 15 puzzle game? The sequence must guarantee the game be solvable. The game will be implemented in C++.

I want to make a 15 puzzle game where repeated numbers are not allowed. An arbitary permutation of numbers, e.g., as returned by std::random_shuffle, is not acceptable, as it may render the game unsolvable. So I want unique numbers from 1 to 15 arranged randomly but in a way that they create a solvable puzzle game. Link to the game: https://15puzzle.netlify.app/

A simple spring-boot-kafka which consumes from a topic on a network cluster:

Errors:

Bootstrap broker localhost:9092 (id: -1 rack: null) disconnected

Connection to node -1 (localhost/127.0.0.1:9092) could not be established. Broker may not be available.

Puzzle:

The configured broker is not local, it's BROKER_1.FOO.NET:9094, and it is available.

pom.xml

Background (TL;DR – the original post)

I am currently really struggling with this problem in C and I am wondering if anyone knows what do do. I need to print all possible solutions to a cryptarithmetic problem like BASE + BALL = GAMES. For example one solution here is: A=4 B=7 E=3 G=1 L=5 S=8 M=9 which corresponds to 7483 +7455= 14938. So my task is to find the correct digit to character mapping for this to be true. I can use digits from 0-9 and each digit can only be assigned to one letter. The solution needs to be recursive btw. My thinking process was to find all the unique characters from the 3 strings and assign them a digit and then check if the solution to the above relationship is true. In case it's not true I need to try a different combination of digits to characters. I just don't know what method I need to use to cover all possible combinations. I don't necessarily want the code, I am just looking for someone to explain to me the algorithmic logic begind it or provide any possible resources.

Edit: What I mean by cryptarithmetic problem is a problem where the user gives as input 3 strings that create an equation like SEND + MORE = MONEY. This equation is solved by assigning a unique digit from 0-9 to each letter like I showed in the example above.

So we want a program to do something like this:

Input : s1 = SEND, s2 = "MORE", s3 = "MONEY"
Output : One of the possible solution is:
D=1 E=5 M=0 N=3 O=8 R=2 S=7 Y=6

If you try to replace each character with it's assigned digit you will see that the equation created holds true. I need a program to do exactly that, meaning to find the correct mapping of digits to character so that the equation produced will be true.

Actual question

The actual question is just about seeking possible assignments of numbers to letters, not about solving the cryptarithmic puzzle in general. It is:

How to generate all variations of length k from the set of ten single-digit non-negative numbers?

In other words, find all sequences of length k (for some 0 < k ≤ 10) of integer numbers 0 through 9, with no repeating numbers within a sequence.

I'm trying to find an alternative to using the Restart Manager for checking if a file is locked. I found this accepted answer to the same question. However, the accepted answer contains the following comment that I do not understand: "this solution will not work if the file doesn't have a Write or Read lock on it, i.e. it has been opened (for reading or writing) with FileShare.Read or FileShare.Write access."

I tested this using the following code (ommitted using blocks and Close() for brevity):

I'm trying to make a simple puzzle system for a game involving beams of light and mirrors in Unity. The light beams are created using an empty GameObject that casts a Raycast2D and uses a LineRenderer to display the beam. When a beam collides with a mirror object I simply use Vector2.Reflect to calculate the new direction.

The implementation works fine when the mirrors are static. When I try to move them around in-game, it causes random stack overflow errors, and there doesn't seem to be a pattern. Here's an example of a working mirror setup:

Here's what happens when I try to move a mirror:

I'm guessing it's due to the mirror somehow reflecting the beam back and causing an infinite reflection loop, but I'm not sure why that would happen.

Relevant code:

This might be an easy question but I was unfortunately not able to find the answer on Google.

Context:
I am working on a project of my own, and I am externalizing some code in a gem (FrenchTaxSystem). It is the first I create a gem and I have difficulties using it properly.

Problem:
When calling a method (like testit) defined in the main file (french_tax_system.rb) of my gem I get a "NoMethodError: undefined method `testit' for FrenchTaxSystem:Module", though I can call constants from this same file (like FISCAL_NB_PARTS_FOR_MARRIED_COUPLE) and it puzzles me.

E.g in IRB I get that when calling a method: [ And it is the same in my Rspecs tests inside my gem

However when calling a constant I have no error:

Main file in my gem:
french_tax_system.rb

New to Selenium and web stuff in general and I am running into an element not found problem trying to find and element with XPath.

selenium.common.exceptions.NoSuchElementException

I've been trying to figure it for a bit, but i cant seem to puzzle it out. Apologize in advance if I've missed something obvious. But if it is a simple google to figure out, i haven't come across the term yet.

When I look with inspect element I get the following two options for the XPath

I have a fairly simple nested array of objects. Each object is composed of 5 (string) values, e.g. ["0,0", "0,0", "0,0", "0,0", "0,1"]. There are no variables attached, hence using arrays inside an array.

Each object represents a puzzle solve permutation being tested by other parts my code. The main data set is composed of 150k permutations.

I am really puzzled about Vaadin's Tabs/Tab-component:

I have created a page with a couple of tabs essentially like this: