# Blog

## How to Solve the Traveling Salesman Problem in Kotlin

This problem is NP-hard, which means that there is no known polynomial-time algorithm to find the optimal solution. However, there are many heuristics and exact algorithms that can solve the problem for small or medium-sized instances, or approximate the solution for large instances.

## Brute Force

The simplest way to solve the TSP is to generate all possible permutations of the cities and calculate the cost of each one. Then, we can return the permutation with the minimum cost as the optimal solution.

This method is guaranteed to find the optimal solution, but it is very inefficient. The number of permutations grows factorially with the number of cities, so for n cities, there are n! possible routes. For example, if we have 10 cities, there are 10! = 3,628,800 possible routes. If we have 20 cities, there are 20! = 2.43 x 10^18 possible routes.

To implement this method in Kotlin, we can use a vector to store all the cities except the starting city. Then, we can use the nextPermutation function from the Kotlin standard library to generate all possible permutations of this vector. For each permutation, we can calculate the cost by adding up the distances between consecutive cities and between the last city and the starting city. We can keep track of the minimum cost and the corresponding permutation using two variables. Finally, we can return the permutation with the minimum cost as the optimal solution.

Here is an example of how this method looks like in code:

`// A function that calculates the cost of a route fun calculateCost(graph: Array<IntArray>, route: List<Int>, start: Int): Int { var cost = 0 var current = start for (city in route) { cost += graph[current][city] current = city } cost += graph[current][start] return cost } // A function that solves the TSP using brute force fun solveTSPBruteForce(graph: Array<IntArray>, start: Int): List<Int> { // Create a vector of all cities except the start val cities = mutableListOf<Int>() for (i in graph.indices) { if (i != start) { cities.add(i) } } // Initialize the minimum cost and the optimal route var minCost = Int.MAX_VALUE var optimalRoute = listOf<Int>() // Generate all permutations of cities do { // Calculate the cost of the current permutation val cost = calculateCost(graph, cities, start) // Update the minimum cost and the optimal route if needed if (cost < minCost) { minCost = cost optimalRoute = cities.toList() } } while (cities.nextPermutation()) // Return the optimal route return optimalRoute } `

## Nearest Neighbor

A more efficient way to solve the TSP is to use a heuristic that builds a route by choosing the nearest city at each step. This method is not guaranteed to find the optimal solution, but it is much faster than brute force.

The idea is to start from any city and mark it as visited. Then, find the nearest unvisited city and move to it. Repeat this process until all cities are visited. Finally, return to the starting city to complete the route.

This method has a time complexity of O(n^2), where n is the number of cities. This is because we need to loop through all cities and find the nearest unvisited city at each step.

To implement this method in Kotlin, we can use a boolean array to keep track of which cities are visited. Then, we can use a loop to iterate through all cities and find the nearest unvisited city using a nested loop. We can add each city to a list as we visit them. Finally, we can return the list as the solution.

Here is an example of how this method looks like in code:

`// A function that solves the TSP using nearest neighbor heuristic fun solveTSPNearestNeighbor(graph: Array<IntArray>, start: Int): List<Int> { // Create an array of visited cities val visited = BooleanArray(graph.size) { false } // Mark the start city as visited visited[start] = true // Create a list to store the route val route = mutableListOf<Int>() // Add the start city to the route route.add(start) // Initialize the current city as start var current = start // Loop until all cities are visited while (route.size < graph.size) { // Initialize the minimum distance and the nearest city var minDistance = Int.MAX_VALUE var nearestCity = -1 // Loop through all cities for (i in graph.indices) { // Skip if the city is visited or same as current if (visited[i] || i == current) continue // Update the minimum distance and nearest city if needed if (graph[current][i] < minDistance) { minDistance = graph[current][i] nearestCity = i } } // Mark the nearest city as visited visited[nearestCity] = true // Add it to the route route.add(nearestCity) // Update current city as nearest city current = nearestCity } // Return route return route } `

## Dynamic Programming

A more advanced way to solve the TSP is to use a dynamic programming algorithm that exploits the overlapping subproblems and optimal substructure of the problem. This method can find the optimal solution in polynomial time, but it requires a lot of memory.

The idea is to use a two-dimensional array to store the minimum cost of visiting a subset of cities and ending at a specific city. The array is indexed by a bitmask that represents the subset of cities and an integer that represents the last city. The base case is when the subset contains only one city, which is the starting city. The cost is zero in this case. The recursive case is when the subset contains more than one city. The cost is the minimum of the cost of visiting the previous subset and ending at any other city plus the distance from that city to the current city.

This method has a time complexity of O(n^2 * 2^n), where n is the number of cities. This is because we need to fill up the array for all possible subsets of cities and all possible last cities. The array has a size of 2^n * n.

To implement this method in Kotlin, we can use a nested function that takes a bitmask and a last city as parameters and returns the minimum cost. The function can use memoization to avoid repeated calculations. Then, we can call the function with the bitmask that represents all cities and the starting city as parameters. We can also use another array to store the optimal route by keeping track of which city was chosen at each step.

Here is an example of how this method looks like in code:

`// A function that solves the TSP using dynamic programming fun solveTSPDynamicProgramming(graph: Array<IntArray>, start: Int): List<Int> { // Create an array for memoization val memo = Array(1 shl graph.size) { IntArray(graph.size) { -1 } } // Create an array for storing the route val route = Array(1 shl graph.size) { IntArray(graph.size) { -1 } } // A nested function that takes a bitmask and a last city and returns the minimum cost fun dp(bitmask: Int, last: Int): Int { // Base case: if only one city in the subset, return zero if (bitmask == (1 shl last)) return 0 // If already calculated, return memoized value if (memo[bitmask][last] != -1) return memo[bitmask][last] // Initialize the minimum cost and the previous city var minCost = Int.MAX_VALUE var prevCity = -1 // Loop through all cities for (i in graph.indices) { // Skip if the city is not in the subset or same as last if ((bitmask and (1 shl i)) == 0 || i == last) continue // Calculate the cost of visiting the previous subset and ending at i val cost = dp(bitmask xor (1 shl last), i) + graph[i][last] // Update the minimum cost and previous city if needed if (cost < minCost) { minCost = cost prevCity = i } } // Memoize and store the minimum cost and previous city memo[bitmask][last] = minCost route[bitmask][last] = prevCity // Return minimum cost return minCost } // Call dp with all cities in the subset and start as last city val minCost = dp((1 shl graph.size) - 1, start) // Create a list to store the optimal route val optimalRoute = mutableListOf<Int>() // Add start to the route optimalRoute.add(start) // Initialize bitmask and last city var bitmask = (1 shl graph.size) - 1 var last = start // Loop until all cities are added to route while (route[bitmask][last] != -1) { // Find previous city from route array val prev = route[bitmask][last] // Add it to route optimalRoute.add(prev) // Update bitmask and last city bitmask = bitmask xor (1 shl last) last = prev } // Return optimal route return optimalRoute } `

## How to Introduce a New Cat into Your Household with Other Cats

If you are thinking of adding a new cat to your family, you may be wondering how to make the introduction process as smooth and stress-free as possible for both the new and the resident cats. Cats are territorial animals and may not welcome a stranger into their home right away. However, with some patience, planning, and positive associations, you can help your cats get along and form a harmonious household. Here are some steps to follow when introducing a new cat to your home:

## Step 1: Separate the cats

Before you bring your new cat home, prepare a separate room for them where they can stay for the first few days or weeks. This room should have everything they need, such as food, water, litter box, bed, scratching post, toys, and hiding places. This will allow your new cat to adjust to their new environment and feel safe and comfortable.

Meanwhile, your resident cat (s) will be able to smell and hear the new cat without seeing them. This will help them get used to the idea of having another cat in the house without feeling threatened or invaded. You can also swap bedding or toys between the cats to help them familiarize themselves with each other’s scent.

## Step 2: Create positive associations

At this point, you have two or more cats who may be curious about each other, but also fearful and/or stressed by the presence of the other. The goal of this step is to create positive associations between the cats by rewarding them with treats, praise, or play whenever they are near each other.

One way to do this is to feed the cats on opposite sides of a closed door. This way, they can smell and hear each other while enjoying a delicious meal. Gradually move the food bowls closer to the door until they are eating next to each other with only a thin barrier between them.

Another way to create positive associations is to use a baby gate or a screen door to allow visual contact between the cats while still keeping them separated. You can also use toys or wand teasers to encourage them to play with each other through the gate or screen.

## Step 3: Supervised time together

When both the new and the resident cat (s) are showing calm and relaxed behavior around each other, you can start letting them interact in the same room under your supervision. Make sure you have plenty of toys, treats, and distractions available to keep them busy and happy.

Start with short sessions of 10-15 minutes and gradually increase the duration and frequency as the cats get more comfortable with each other. Watch for any signs of aggression or fear, such as hissing, growling, swatting, or hiding. If you notice any of these behaviors, separate the cats immediately and go back to the previous step.

## Step 4: Full integration

When the cats are able to coexist peacefully in the same room for extended periods of time without any signs of stress or conflict, you can consider them fully integrated. You can now let them roam freely in the house and share resources such as food bowls, litter boxes, and sleeping areas.

However, keep in mind that some cats may never become best friends or cuddle buddies. Some may prefer to keep their distance or tolerate each other’s presence. As long as they are not fighting or hurting each other, that’s okay too. The most important thing is that they are happy and healthy in their home.

I hope you enjoyed reading this blog post. If you have any questions or comments, please leave them below.

## Top 10 Reasons to Adopt a Cat from a Rescue

If you are thinking of adding a furry friend to your family, you might want to consider adopting a cat from a rescue. There are many benefits of adopting a rescue cat, both for you and the cat. Here are some of the top reasons why you should adopt a cat from a rescue.

## 1. You’ll save more than one life by adopting a cat

Updated

According to the latest research and data, Around 920,000 Shelter Animals are Euthanized each year including 390,000 Dogs and 530,000 Cats.

## 3. The personality of an adopted cat is known

Cats in many shelters interact with their caretakers and volunteers every day, and these people really get to know their personalities3. Particularly with adult cats, you can find a companion with the type of temperament you’re looking for. You could find a playful, active cat or a calmer feline who prefers cuddling and a quieter environment2.

## 10. You’ll experience unconditional love

One of the best reasons to adopt a cat from a rescue is the love they will give you in return5. A rescue cat knows that what you did for them is selfless and wonderful. They will appreciate your kindness and show it in their own ways. Whether it’s by purring on your lap, rubbing against your leg or greeting you at the door, they will make you feel loved every day2.

So what are you waiting for? Visit your local shelter or rescue today and find your purr-fect match!

## Structural Design Patterns in Android Kotlin

Structural design patterns are all about how you compose objects and classes to obtain new functionality. They help you simplify the design by finding a simple way of realizing relationships between entities1. In this blog post, we will cover three common structural design patterns: adapter, decorator and facade. We will also see how to implement them in Kotlin using some of its features such as extension functions, data classes and delegation.

The adapter pattern allows you to convert the interface of a class into another interface that clients expect. It lets you make incompatible classes work together by wrapping one of them with an adapter class that implements the desired interface2. For example, suppose you have a class that represents a book:`data class Book(val title: String, val author: String, val pages: Int) `Copy

And you have another class that represents a library:`class Library { private val books = mutableListOf<Book>() fun addBook(book: Book) { books.add(book) } fun getBooks(): List<Book> { return books } } `Copy

Now, suppose you want to use a third-party library that provides a function to print a list of books in a nice format. However, this function expects a list of objects that implement the Printable interface:`interface Printable { fun print(): String } `Copy

How can you make your Book class compatible with this function? One way is to use the adapter pattern. You can create an adapter class that implements Printable and wraps a Book object:`class BookAdapter(private val book: Book) : Printable { override fun print(): String { return "Title: \${book.title}, Author: \${book.author}, Pages: \${book.pages}" } } `Copy

Then, you can use this adapter class to convert your list of books into a list of printable objects:`val library = Library() library.addBook(Book("The Lord of the Rings", "J.R.R. Tolkien", 1178)) library.addBook(Book("Harry Potter and the Philosopher's Stone", "J.K. Rowling", 223)) library.addBook(Book("The Hitchhiker's Guide to the Galaxy", "Douglas Adams", 180)) val printables = library.getBooks().map { book -> BookAdapter(book) } printBooks(printables) // This is the third-party function that expects a list of Printable objects `Copy

Alternatively, you can use an extension function to achieve the same result without creating an adapter class:`fun Book.toPrintable(): Printable { return object : Printable { override fun print(): String { return "Title: \${this@toPrintable.title}, Author: \${this@toPrintable.author}, Pages: \${this@toPrintable.pages}" } } } val printables = library.getBooks().map { book -> book.toPrintable() } printBooks(printables) `Copy

The advantage of using an extension function is that it reduces the amount of code and classes needed. However, it may not be suitable for complex scenarios where you need more control over the adaptation logic.

## Decorator Pattern

The decorator pattern allows you to add new behavior or functionality to an existing object without modifying its structure or subclassing it. It lets you wrap an object with another object that implements the same interface and delegates all the requests to the original object while adding some extra logic before or after2. For example, suppose you have an interface that represents a coffee:`interface Coffee { fun cost(): Double fun description(): String } `Copy

And you have a concrete class that implements this interface:`class Espresso : Coffee { override fun cost(): Double { return 1.5 } override fun description(): String { return "Espresso" } } `Copy

Now, suppose you want to add some extra ingredients to your coffee, such as milk, whipped cream or caramel. One way is to use the decorator pattern. You can create an abstract class that implements Coffee and wraps another Coffee object:`abstract class CoffeeDecorator(private val coffee: Coffee) : Coffee { override fun cost(): Double { return coffee.cost() } override fun description(): String { return coffee.description() } } `Copy

Then, you can create concrete subclasses that extend this abstract class and add their own logic:`class Milk(private val coffee: Coffee) : CoffeeDecorator(coffee) { override fun cost(): Double { return super.cost() + 0.5 } override fun description(): String { return "\${super.description()}, Milk" } } class WhippedCream(private val coffee: Coffee) : CoffeeDecorator(coffee) { override fun cost(): Double { return super.cost() + 0.7 } override fun description(): String { return "\${super.description()}, Whipped Cream" } } class Caramel(private val coffee: Coffee) : CoffeeDecorator(coffee) { override fun cost(): Double { return super.cost() + 0.8 } override fun description(): String { return "\${super.description()}, Caramel" } } `Copy

Then, you can use these decorator classes to create different combinations of coffee:`val espresso = Espresso() println("\${espresso.description()} costs \${espresso.cost()}") // Espresso costs 1.5 val espressoWithMilk = Milk(espresso) println("\${espressoWithMilk.description()} costs \${espressoWithMilk.cost()}") // Espresso, Milk costs 2.0 val espressoWithMilkAndWhippedCream = WhippedCream(espressoWithMilk) println("\${espressoWithMilkAndWhippedCream.description()} costs \${espressoWithMilkAndWhippedCream.cost()}") // Espresso, Milk, Whipped Cream costs 2.7 val espressoWithMilkAndWhippedCreamAndCaramel = Caramel(espressoWithMilkAndWhippedCream) println("\${espressoWithMilkAndWhippedCreamAndCaramel.description()} costs \${espressoWithMilkAndWhippedCreamAndCaramel.cost()}") // Espresso, Milk, Whipped Cream, Caramel costs 3.5 `Copy

Alternatively, you can use delegation instead of inheritance to implement the decorator pattern in Kotlin. You can create an interface that represents a decorator:`interface Decorator<T> : T { val delegate: T } `Copy

Then, you can create concrete classes that implement this interface and delegate all the requests to the wrapped object while adding their own logic:`class Milk(override val delegate: Coffee) : Decorator<Coffee>, Coffee by delegate { override fun cost(): Double { return delegate.cost() + 0.5 } override fun description(): String { return "\${delegate.description()}, Milk" } } class WhippedCream(override val delegate: Coffee) : Decorator<Coffee>, Coffee by delegate { override fun cost(): Double { return delegate.cost() + 0.7 } override fun description(): String { return "\${delegate.description()}, Whipped Cream" } } class Caramel(override val delegate: Coffee) : Decorator<Coffee>, Coffee by delegate { override fun cost(): Double { return delegate.cost() + 0.8 } override fun description(): String { return "\${delegate.description()}, Caramel" } } `Copy

Then, you can use these decorator classes to create different combinations of coffee as before:`val espresso = Espresso() println("\${espresso.description()} costs \${espresso.cost()}") // Espresso costs 1.5 val espressoWithMilk = Milk(espresso) println("\${espressoWithMilk.description()} costs \${espressoWithMilk.cost()}") // Espresso, Milk costs 2.0 val espressoWithMilkAndWhippedCream = WhippedCream(espressoWithMilk) println("\${espressoWithMilkAndWhippedCream.description()} costs \${espressoWithMilkAndWhippedCream.cost()}") // Espresso, Milk, Whipped Cream costs 2.7 val espressoWithMilkAndWhippedCreamAndCaramel = Caramel(espressoWithMilkAndWhippedCream) println("\${espressoWithMilkAndWhippedCreamAndCaramel.description()} costs \${espressoWithMilkAndWhippedCreamAndCaramel.cost()}") // Espresso, Milk, Whipped Cream, Caramel costs 3.5 `Copy

The advantage of using delegation is that it avoids creating unnecessary subclasses and makes the code more concise and readable.

The facade pattern simplifies the interaction with a complex system or library by providing a unified and easy-to-use interface. It hides the details and implementation of the system from the clients and exposes only the essential functionality. For example, suppose you have a complex library that offers various functions for image processing:`class ImageProcessingLibrary { fun loadBitmap(path: String): Bitmap { ... } fun resizeBitmap(bitmap: Bitmap, width: Int, height: Int): Bitmap { ... } fun cropBitmap(bitmap: Bitmap, x: Int, y: Int, width: Int, height: Int): Bitmap { ... } fun applyFilter(bitmap: Bitmap, filter: Filter): Bitmap { ... } fun saveBitmap(bitmap: Bitmap, path: String) { ... } // ... more functions } `Copy

Using this library directly may be cumbersome and error-prone for the clients. They need to know how to use each function correctly and in what order. For example, if they want to load an image from a file, resize it, apply a filter and save it back to another file, they need to write something like this:`val library = ImageProcessingLibrary() val bitmap = library.loadBitmap("input.jpg") val resizedBitmap = library.resizeBitmap(bitmap, 300, 300) val filteredBitmap = library.applyFilter(resizedBitmap, Filter.GRAYSCALE) library.saveBitmap(filteredBitmap, "output.jpg") `Copy

To make this task easier and more convenient, you can use the facade pattern. You can create a class that acts as a facade for the library and provides a simple interface for common operations:`class ImageProcessor(private val library: ImageProcessingLibrary) { fun processImage(inputPath: String, outputPath: String, width: Int, height: Int, filter: Filter) { val bitmap = library.loadBitmap(inputPath) val resizedBitmap = library.resizeBitmap(bitmap, width, height) val filteredBitmap = library.applyFilter(resizedBitmap, filter) library.saveBitmap(filteredBitmap, outputPath) } // ... more functions for other operations } `Copy

Then, the clients can use this facade class to perform the same operation with less code and complexity:`val processor = ImageProcessor(ImageProcessingLibrary()) processor.processImage("input.jpg", "output.jpg", 300, 300, Filter.GRAYSCALE) `Copy

The advantage of using the facade pattern is that it reduces the coupling between the clients and the system or library. It also improves the readability and maintainability of the code by encapsulating the logic and details of the system or library in one place.

# Conclusion

In this blog post, we have learned about three common structural design patterns: adapter, decorator and facade. We have seen how they can help us simplify the design and implementation of our Android applications by composing objects and classes in different ways. We have also seen how to implement them in Kotlin using some of its features such as extension functions, data classes and delegation. We hope you have enjoyed this post and found it useful. If you have any questions or feedback, please feel free to leave a comment below. Happy coding!

## A New Star in the Night Sky: How to See the Supernova in the Pinwheel Galaxy

Have you ever wondered what it would be like to witness a star exploding? Well, now you have a chance to see it for yourself, thanks to a new supernova that has appeared in the Pinwheel Galaxy, also known as Messier 101 or M101. This is the closest supernova to Earth in a decade, and it’s visible with a small telescope or even binoculars.

What is a supernova?
A supernova is a powerful explosion that occurs when a massive star runs out of fuel and collapses under its own gravity. The core of the star implodes, creating a shock wave that blasts the outer layers of the star into space. The resulting explosion can outshine an entire galaxy for a brief period of time, releasing enormous amounts of energy and radiation.

Supernovae are rare events in our galaxy, occurring only once every few centuries. However, they are more common in other galaxies, especially those that have a lot of young and massive stars. The Pinwheel Galaxy is one such galaxy, located about 21 million light-years away from Earth in the constellation of Ursa Major. It is a spiral galaxy with four prominent arms that resemble a pinwheel.

How was the supernova discovered?
The new supernova in the Pinwheel Galaxy was discovered on May 19, 2023 by Koichi Itagaki, an amateur astronomer from Japan. He noticed a bright spot of light near the end of one of the galaxy’s arms that was not there before. He reported his observation to the Transient Name Server (TNS), an online database that collects and verifies reports of new astronomical phenomena.

The supernova was soon confirmed by other astronomers around the world, who named it SN 2023ixf. According to Andy Howell, an astronomer at the University of California, Santa Barbara, SN 2023ixf is most likely a type II supernova, which means that it resulted from the core collapse of a massive star at the end of its life. The star that exploded was probably about 10 times more massive than our sun.

How can you see the supernova?
SN 2023ixf is currently visible in the night sky, and it should continue to brighten for a few days before fading away over the next few months. To see it, you will need a telescope or binoculars with at least 50x magnification. You will also need a clear and dark sky, away from city lights and pollution.

To find the Pinwheel Galaxy, you can use the Big Dipper as a guide. The Big Dipper is part of Ursa Major, one of the most recognizable constellations in the northern hemisphere. It looks like a large ladle with four stars forming the bowl and three stars forming the handle. The Pinwheel Galaxy is located about halfway between the two stars at the end of the handle, Mizar and Alkaid. You can use your fist held at arm’s length to measure about 10 degrees of sky between these two stars.

Once you have located the Pinwheel Galaxy, you can look for SN 2023ixf near the end of one of its spiral arms. It should appear as a bright point of light that stands out from the rest of the galaxy. You can compare your view with images taken by professional and amateur astronomers online to make sure you are looking at the right spot.

Why is this supernova important?
SN 2023ixf is not only a spectacular sight for skywatchers, but also a valuable source of information for scientists. Supernovae are important for understanding how stars evolve and die, how galaxies form and change over time, and how elements are created and distributed throughout the universe.

By observing SN 2023ixf, astronomers can learn more about its progenitor star, such as its mass, composition, age, and environment. They can also measure how fast and how far the supernova expands, how much energy and radiation it emits, and what kind of remnants it leaves behind. These data can help them test and refine their theories and models of stellar evolution and explosion.

Moreover, SN 2023ixf can provide clues about the history and structure of the Pinwheel Galaxy itself. By comparing its brightness and distance with other supernovae in other galaxies, astronomers can estimate how far away M101 is from us more accurately. They can also use SN 2023ixf as a probe to study how dust and gas affect its light as it travels through different regions of M101.

Don’t miss this opportunity!
SN 2023ixf is a rare and exciting event that you don’t want to miss. Grab your telescope or binoculars and head outside to witness a star exploding in another galaxy. You will be amazed by what you see!

## The Necessity of Cat Rescues

Cat rescues are a vital part of helping homeless cats find loving homes. There are many reasons why cat rescues are necessary, ranging from providing neonate kittens with lifesaving care to exposing long-term shelter residents to new groups of potential adopters 1.

One of the key reasons why cat rescues are necessary is that they save the lives of neonate and pee wee kittens. These kittens are extremely vulnerable and often don’t survive without round-the-clock care. Some shelters and rescue organizations run fostering programs, in which they train and supply foster caregivers with what they need to keep kittens healthy enough to be spay/neutered and ultimately adopted 1.

Fostering also provides a safe and healthy environment for kittens to grow. With weaker immune systems, kittens are more prone to getting sick in shelter settings where they are exposed to various animals. Kittens under eight weeks old—who cannot survive on their own without continuous care—are especially vulnerable 1.

Cats living in a home often receive more attention, which helps relieve their stress. Studies show that increases in socialization and play time are good for kittens’ mental and physical health, which also increases their chances for eventual adoption 1.

Fostered kittens are likely to be better sensitized to the world they’ll face when adopted. Spending time with people, children and other domestic dynamics in a temporary home enables cats—especially kittens—to become comfortable with similar stimuli in a permanent home 1.

In conclusion, cat rescues play an important role in helping homeless cats find loving homes. By fostering or adopting a cat from a shelter, you can make a big difference in the life of an animal in need.

## The Smore Without Chocolate

Once upon a time, there was a s’more named Sammy. Sammy was made up of two graham crackers, a marshmallow, and a piece of chocolate. But one day, when Sammy was being made, there was no chocolate left!

Sammy was very sad. He thought he would never be able to taste as good as the other s’mores. But then he had an idea. Instead of using chocolate, he used two cookies instead of graham crackers.

At first, everyone laughed at Sammy. They thought he was crazy for using cookies instead of graham crackers. But then they tried his s’more and were amazed! It was the best s’more they had ever tasted.

From that day on, Sammy became famous for his delicious s’mores. Everyone wanted to try them and he even started his own s’more stand.

And that’s the story of how Sammy the s’more became famous for using cookies instead of graham crackers.

I hope you enjoyed that story! Do you have any other requests?

## Scary Campfire Story

It was a dark and stormy night. A group of friends were camping in the woods. They had set up their tents and started a campfire. They were roasting marshmallows and telling ghost stories when they heard a rustling in the bushes.

At first, they thought it was just the wind. But then they heard it again. This time it was louder. They looked around but couldn’t see anything.

Suddenly, they heard a loud growl. It was coming from the woods. They all froze in fear. Then they saw it – a huge grizzly bear was standing right in front of them.

The bear was massive and looked angry. It started to move towards them slowly. The friends tried to run but it was too late. The bear caught up with them and attacked.

The friends fought back as hard as they could but the bear was too strong. One by one, they fell to the ground. The bear mauled them all to death.

The next morning, when the park rangers found their campsite, there was no sign of the friends except for their torn tents and scattered belongings.

The rangers searched for days but never found any trace of the missing campers. Some say that their spirits still haunt the woods to this day.

I hope you enjoyed that story! Do you have any other requests?

## Onomatopoeia

Onomatopoeia is a word that sounds like what it means. They help you hear what is going on. For example, “thud”, “crash”, “bang” and “buzz” are all examples of onomatopoeia. Animal sounds are often onomatopoeic: “roar”, “meow”, “moo”, “cluck”, “oink”1.

Here are some more examples of onomatopoeia:

Buzz: the sound of a bee
Sizzle: the sound of frying food
Hiss: the sound of a snake
Splash: the sound of water hitting something
Crackle: the sound of fire burning
I hope this helps you get started with your blog post! Let me know if you have any other questions.

## Creational Design Patterns in Kotlin Android

Creational design patterns are a set of solutions to common software development problems that deal with how objects are being created. Using such patterns will ensure that your code is flexible and reusable, and that you avoid hard-coded dependencies and tight coupling between classes.

In this blog post, I will show you some of the most important and widely used creational design patterns in Kotlin Android. You will learn how to apply these patterns to your projects and how they can help you write better and more maintainable code. I will cover four creational design patterns:

• Factory and abstract factory (provider model) method
• Singleton
• Builder
• Dependency injection

## Factory and abstract factory (provider model) method

The factory method pattern defines an interface for creating an object, but lets subclasses decide which class to instantiate. The abstract factory pattern provides an interface for creating families of related or dependent objects without specifying their concrete classes.

These patterns are useful when you want to decouple the creation of objects from their usage, or when you want to provide different implementations of the same interface depending on some conditions. For example, you can use these patterns to create different types of views or fragments based on the device configuration or user preferences.

In Kotlin, you can use the provider model to implement these patterns. The provider model is a way of creating objects using lambda expressions or function references that act as factories. For example, you can use a provider function to create different types of fragments based on a parameter:

`// An interface for fragments that display some content interface ContentFragment { fun showContent(content: String) } // A concrete implementation of ContentFragment that shows content in a text view class TextFragment : Fragment(), ContentFragment { private lateinit var textView: TextView override fun onCreateView( inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle? ): View? { return inflater.inflate(R.layout.text_fragment, container, false) } override fun onViewCreated(view: View, savedInstanceState: Bundle?) { super.onViewCreated(view, savedInstanceState) textView = view.findViewById(R.id.text_view) } override fun showContent(content: String) { textView.text = content } } // Another concrete implementation of ContentFragment that shows content in a web view class WebFragment : Fragment(), ContentFragment { private lateinit var webView: WebView override fun onCreateView( inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle? ): View? { return inflater.inflate(R.layout.web_fragment, container, false) } override fun onViewCreated(view: View, savedInstanceState: Bundle?) { super.onViewCreated(view, savedInstanceState) webView = view.findViewById(R.id.web_view) } override fun showContent(content: String) { webView.loadUrl(content) } } // A provider function that returns a ContentFragment based on a parameter fun provideContentFragment(type: String): ContentFragment = when (type) { "text" -> TextFragment() "web" -> WebFragment() else -> throw IllegalArgumentException("Unknown type: \$type") } `

## Singleton

The singleton pattern ensures that a class has only one instance and provides a global point of access to it. This pattern is useful when you want to have a single source of truth for some data or functionality in your app. For example, you can use this pattern to create a repository that handles data access from different sources.

In Kotlin, you can use the object declaration to create a singleton class. The object declaration combines a class declaration and a single instance of that class into one expression. For example, you can use an object declaration to create a news repository that fetches data from a remote data source:

`// A singleton class that acts as a repository for news data object NewsRepository { // A reference to the remote data source private val newsRemoteDataSource = // getDataSource() // A flow that emits the latest news from the remote data source val latestNews: Flow<List<ArticleHeadline>> = newsRemoteDataSource.latestNews // A function that returns the details of an article by its id suspend fun getArticleDetails(id: String): ArticleDetails { return newsRemoteDataSource.getArticleDetails(id) } } `

## Builder

The builder pattern separates the construction of a complex object from its representation so that the same construction process can create different representations. This pattern is useful when you want to create objects with many optional parameters or when you want to have more control over how the object is constructed. For example, you can use this pattern to create an alert dialog with various options.

In Kotlin, you can use named arguments and default values to implement this pattern. Named arguments allow you to specify the name of a parameter when calling a function, which makes the code more readable and avoids errors when there are many parameters. Default values allow you to omit some parameters when calling a function if they have a predefined value. For example, you can use named arguments and default values to create an alert dialog builder class:

`// A class that represents an alert dialog with various options class AlertDialog( val title: String, val message: String, val positiveButton: String = "OK", val negativeButton: String? = null, val icon: Int? = null, val onPositiveClick: () -> Unit = {}, val onNegativeClick: () -> Unit = {} ) { // A function that shows the alert dialog on the screen fun show() { // Create and display an alert dialog using the Android SDK ... } } // A builder class that creates an AlertDialog instance using named arguments and default values class AlertDialogBuilder { // A function that returns an AlertDialog instance with the given parameters fun build( title: String, message: String, positiveButton: String = "OK", negativeButton: String? = null, icon: Int? = null, onPositiveClick: () -> Unit = {}, onNegativeClick: () -> Unit = {} ): AlertDialog { return AlertDialog( title = title, message = message, positiveButton = positiveButton, negativeButton = negativeButton, icon = icon, onPositiveClick = onPositiveClick, onNegativeClick = onNegativeClick ) } } `

## Dependency injection

The dependency injection pattern is a technique whereby one object supplies the dependencies of another object. A dependency is an object that can be used (a service). An injection is the passing of a dependency to a dependent object (a client) that would use it.

This pattern is useful when you want to reduce coupling and increase testability between classes by delegating the responsibility of creating and providing dependencies to another object or framework. For example, you can use this pattern to inject dependencies into your activities or view models.

In Kotlin Android, you can use frameworks like Dagger or Koin to implement this pattern. These frameworks provide annotations or DSLs to define dependencies and inject them into your classes. For example, you can use Koin to inject dependencies into your view model:

`// A class that represents a user profile view model with some dependencies class UserProfileViewModel( private val userRepository: UserRepository, private val analyticsService: AnalyticsService ) : ViewModel() { // Some view model logic using userRepository and analyticsService ... } // A module that defines dependencies using Koin DSL val appModule = module { // Define UserRepository as a singleton using factory function single<UserRepository> { UserRepositoryImpl(get()) } // Define AnalyticsService as a singleton using constructor injection single<AnalyticsService> { AnalyticsServiceImpl() } // Define UserProfileViewModel using constructor injection viewModel { UserProfileViewModel(get(), get()) } } // Start Koin with appModule in Application class class MyApp : Application() { override fun onCreate() { super.onCreate() startKoin { androidContext(this@MyApp) modules(appModule) } } } // Get UserProfileViewModel instance using Koin extension function in Activity class class UserProfileActivity : AppCompatActivity() { // Inject UserProfileViewModel private val viewModel by viewModel<UserProfileViewModel>() override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_user_profile) // Use viewModel ... } } `

## Conclusion

In this blog post, you learned how to use creational design patterns in Kotlin Android. You learned how to apply these patterns to your projects and how they can help you write better and more maintainable code. You learned how to use factory and abstract factory (provider model) method, singleton, builder, and dependency injection patterns.

If you want to learn more about design patterns and other Kotlin features for Android development, check out these resources:

I hope you enjoyed this blog post and found it useful. Happy coding! 😊