One Generation of a Genetic Algorithm

A genetic algorithm improves a population of candidate solutions the way evolution does: select fit parents, combine them, and add random mutations. Here the candidates are bit strings and fitness is the number of 1s (the OneMax problem).

To make it testable, every random choice is given. With N strings (N is even), build N children in pairs. For pair k = 0, 1, …, N/2 - 1:

Selection: parent1 wins tournament tournaments[2k] and parent2 wins tournaments[2k + 1]. A tournament [i, j] is won by whichever of population[i] and population[j] has more 1s; on a tie, population[i] wins.
Crossover at c = crossover_points[k]: child 2k = parent1[0:c] + parent2[c:] and child 2k + 1 = parent2[0:c] + parent1[c:].

Then apply each mutation [child, position] in order by flipping that bit of that child.

Implement ga_generation(population, tournaments, crossover_points, mutations).

Input

population: N bit strings of equal length L.

tournaments: N pairs of population indices.

crossover_points: N/2 cut points, each between 1 and L - 1.

mutations: [child, position] pairs (may be empty).

Output

Return the N children in order.

Constraints

2 ≤ N ≤ 200 (N even), 2 ≤ L ≤ 64

0 ≤ number of mutations ≤ 1,000

Examples

Example 1

Input:
population = ["0000", "1111", "1100", "0011"]
tournaments = [
    [0, 1],
    [2, 3],
    [1, 2],
    [0, 3]
]
crossover_points = [2, 1]
mutations = [
    [0, 0]
]

Expected output:
["0100", "1111", "1011", "0111"]

Explanation

Pair 0: "1111" beats "0000", and "1100" ties "0011" so the first one wins. Cutting after 2 bits gives "1100" and "1111". Pair 1: parents "1111" and "0011", cut after 1 bit: "1011" and "0111". Finally child 0 has bit 0 flipped: "0100".

Example 2

Input:
population = ["10", "01"]
tournaments = [
    [0, 1],
    [1, 0]
]
crossover_points = [1]
mutations = []

Expected output:
["11", "00"]

Explanation

Both strings have one 1, so each tournament is won by its first index: parent1 = "10" and parent2 = "01". Cutting after 1 bit gives "11" and "00".

References

Run the sample tests to check your code without submitting.

Example 1 Not run

Input:

population = ["0000", "1111", "1100", "0011"]
tournaments = [
    [0, 1],
    [2, 3],
    [1, 2],
    [0, 3]
]
crossover_points = [2, 1]
mutations = [
    [0, 0]
]

Expected output:

["0100", "1111", "1011", "0111"]

Your output

Example 2 Not run

Input:

population = ["10", "01"]
tournaments = [
    [0, 1],
    [1, 0]
]
crossover_points = [1]
mutations = []

Expected output:

["11", "00"]

Your output

4 hidden tests also run when you submit. If your code fails one, you'll see that test. Solve the challenge to see them all.

Online Kotlin Compiler

Write, compile, run, and debug Kotlin code online in a full-featured browser IDE. Work with multiple files, save your workspace, and collaborate in real time.

Version

Pre-installed Libs

🚀 71,457 total executions (576 this month)

Output

Practice Kotlin with coding challenges

Solve hands-on problems right in this editor: run the sample tests, submit, and get an AI code review.

All Kotlin challenges

Easy

Rectangle Perimeter

Compute the perimeter of a rectangle from its sides.

You'll learn ArithmeticReturn values

BeginnerLearning-pathVariables

View solutions (12)

Easy

Distance Between Points

Compute the straight-line distance between two points.

You'll learn Pythagorean theoremSquare roots

BeginnerFunctionsLearning-pathmath

View solutions (7)

Easy

Days in a Month

Return how many days a month has, including leap years.

You'll learn Calendar rulesHelper functions

BeginnerConditionsFunctionsLearning-path

View solutions (6)

Easy

Average of Three

Average three whole numbers.

You'll learn ArithmeticDivision

BeginnerLearning-pathVariables

View solutions (6)

Easy

Dot Product of Two Vectors

Multiply two vectors element by element and add the results: the core operation of every neuron.

You'll learn VectorsDot product

Neural networksaimachine learning

View solutions (4)

Easy

Largest of Three

Pick the largest of three numbers without a built-in max.

You'll learn ComparisonsCombining conditions

BeginnerConditionsLearning-path

View solutions (4)

Easy

Prime Number Check

Decide whether a number is prime.

You'll learn DivisibilityLoop optimization

BeginnerLoopsNumbersStudent-beginner

View solutions (3)

Easy

Number Triangle

Build a triangle of increasing numbers.

You'll learn Growing rowsCounters across rows

BeginnerLearning-pathNested-loopsPatterns

View solutions (3)

Easy

Armstrong Number

Check whether a number equals the sum of its digits raised to the digit count.

You'll learn Digit extractionPowers

BeginnerNumbersStudent-beginner

View solutions (3)

Easy

Row Sums

Add up every row of a grid.

You'll learn 2D listsNested loops

BeginnerGridsLearning-path

View solutions (3)

Easy

Min and Max Together

Find the smallest and largest value in one pass.

You'll learn Single passMultiple return values

ArraysBeginnerFunctionsLearning-path

View solutions (3)

Easy

Count Pairs With a Sum

Count pairs of positions whose values add up to a target.

You'll learn Pairs of indexesAvoiding double counts

ArraysBeginnerLearning-pathNested-loops

View solutions (3)

🧩 About This Kotlin Online Executor

The CodeUtility Kotlin Executor lets you write, compile, and run Kotlin code directly in your browser - no installation, IDE, or SDK setup required. It uses real Kotlin compilers running in isolated sandboxes for a safe and authentic execution experience.

This tool supports multiple Kotlin versions - 1.6, 1.9, and 2.1 - so you can explore syntax updates, test code compatibility, and experiment with modern language features like coroutines, data classes, and sealed interfaces.

It’s ideal for students learning Kotlin basics, Android developers experimenting with snippets, or backend engineers testing logic in a JVM environment without leaving the browser.

The environment runs each snippet inside a secure containerized runtime, ensuring consistent performance and safe code execution.

More than a code runner

Use a multi-file editor, an isolated execution terminal, runtime-specific libraries, persistent workspaces, sharing, and real-time collaboration from the same executor.

How to use this executor?

Choose a runtime, open or create a file, write your code, and select Run. Output appears in the terminal, while signed-in users can keep files in a workspace, install libraries, and collaborate through shares.

Select a version and edit the current file or open another workspace file.
Run the code, provide input in the terminal when requested, and review saved run history.
Use libraries, workspace tools, sharing, and chat when your task needs more than one snippet.

Start coding

VersionSelect a runtime before running. Installed libraries belong to the selected language version.
Open files lists unopened text files. Select one to open it in an available editor tab.
Run executes the active file with its workspace available to the program.
Stop ends the current execution before its time limit.
Advanced Mode opens the IDE layout with a file explorer and movable, resizable terminal.

Workspace and libraries

New file creates a file in the selected parent directory and opens it in the editor.
New folder creates a directory, up to the supported nesting depth.
Upload files adds one or more safe files to a directory.
Download saves a file or a zipped directory to your device.
Copy duplicates a workspace file or directory.
Rename changes a file name and updates its open tab and history.
Move relocates an item; files and directories can also be dragged.
Delete removes an item after confirmation and closes its open editor tab.
Pre-installed Libs shows packages already included in this runtime.
Add Lib installs a private package for your account and selected runtime.

Terminal and assistance

Run history opens previous and next saved outputs.
Copy output copies the current terminal text.
Clear output removes all saved run outputs after confirmation.
Explain summarizes the active code.
Recents opens recent explanations and results.
Settings changes fonts, themes, and visible toolbar buttons.

Sharing and collaboration

Share publishes the current file, a directory, or the whole workspace as a snapshot or live workspace. You control link access and who may save changes.
Logs records saved collaborator actions in a shared workspace.
Share chat lets signed-in participants message, mention people, share code blocks, and see online or typing members.
Live collaboration shows collaborator cursors and saved file updates. View-only users can load the latest version or keep temporary edits.

Quotas and limits

Execution time is limited to 20 seconds per server run. Use Stop when you want to end it sooner.
Workspace storage allows 100 files, 100 directories, and 10 MiB total for each signed-in user workspace and language.
Files and folders are limited to 1 MiB per file and 5 nested directory levels. Files generated by your code follow the same quota.
Private libraries are limited to 10 installed packages for each account and runtime.
Share snapshots can contain up to 100 files, 1 MiB per file, and 2 MiB total.
Share invitations support up to 25 people per share, with access and saving permissions managed separately.
Share chat allows 2,000 characters per message and 10,000 messages per share.
Quota enforcement also applies while code is running. A write that exceeds file count, size, storage, or nesting limits is rejected safely.

Good to know Only run code and install packages you trust. Execution is isolated and limited, but your program can still modify files inside a writable workspace up to its enforced quota.

💡 Kotlin Basics Guide for Beginners

1. Declaring Variables and Constants

Kotlin uses val for immutable variables and var for mutable ones.

val name: String = "Alice"
var age: Int = 30
val pi = 3.14  // type inferred

// Constants
const val MAX_USERS = 100

2. Conditionals (if / when)

Use if expressions or when for multiple branches.

val x = 2
if (x == 1) {
    println("One")
} else if (x == 2) {
    println("Two")
} else {
    println("Other")
}

when (x) {
    1 -> println("One")
    2 -> println("Two")
    else -> println("Other")
}

3. Loops

Use for, while, and do-while for iteration.

for (i in 0..2) {
    println(i)
}

var n = 3
while (n > 0) {
    println(n)
    n--
}

4. Arrays

Kotlin supports arrays using the arrayOf() function.

val numbers = arrayOf(10, 20, 30)
println(numbers[1])

5. List Manipulation

Use mutableListOf for dynamic lists.

val nums = mutableListOf(1, 2, 3)
nums.add(4)
nums.removeAt(0)

for (n in nums) {
    print("$n ")
}

6. Console Input/Output

Use readLine() for input and println() for output.

print("Enter your name: ")
val name = readLine()
println("Hello, $name")

7. Functions

Functions use fun keyword with optional return type.

fun add(a: Int, b: Int): Int {
    return a + b
}

println(add(3, 4))

8. Maps

mutableMapOf stores key-value pairs.

val ages = mutableMapOf("Alice" to 30)
println(ages["Alice"])

9. Exception Handling

Use try, catch, and finally to handle errors.

try {
    val result = 10 / 0
} catch (e: ArithmeticException) {
    println("Error: ${e.message}")
}

10. File I/O

Use File from java.io for file operations.

import java.io.File

File("file.txt").writeText("Hello File")
val text = File("file.txt").readText()
println(text)

11. String Manipulation

Kotlin strings support many methods and interpolation.

val text = "Hello World"
println(text.length)
println(text.substring(0, 5))
println(text.contains("World"))

12. Classes & Objects

Kotlin classes are concise and support default constructors.

class Person(val name: String) {
    fun greet() = println("Hi, I'm $name")
}

val p = Person("Alice")
p.greet()

13. Null Safety

Kotlin distinguishes nullable and non-nullable types. Use ? and ?: for safety.

val name: String? = null
println(name?.length ?: 0)