C#•5mo ago

Infinite loop

c#
/// ------------------------------------------------------------
/// <summary>
/// Creates a stack containing unique random numbers</summary>
/// <param name="lower">The lower bound for each number (inclusive)</param>
/// <param name="upper">The upper bound for each number (inclusive)</param>
/// <param name="count">The number of numbers</param>
/// <returns>The stack containing unique random numbers</returns>
/// ------------------------------------------------------------
public static Stack<int> Opdr3RandomNumbers(int lower, int upper, int count)
{
    Stack<int> stack = new Stack<int>();
    HashSet<int> voorgekomenGetallen = new HashSet<int>();

    Random randomNumber = new Random();

    while (stack.Count < count)
    {
        int number = randomNumber.Next(lower, upper);
        bool hasOccurred = occurredNumbers.Contains(number);

        while (hasOccurred) {
            number = randomNumber.Next(lower, upper);
            hasOccurred = occurredNumbers.Contains(number);
        }

        stack.Push(number);
        occurredNumbers.Add(number);
    }

    return stack;
}

c#
/// ------------------------------------------------------------
/// <summary>
/// Creates a stack containing unique random numbers</summary>
/// <param name="lower">The lower bound for each number (inclusive)</param>
/// <param name="upper">The upper bound for each number (inclusive)</param>
/// <param name="count">The number of numbers</param>
/// <returns>The stack containing unique random numbers</returns>
/// ------------------------------------------------------------
public static Stack<int> Opdr3RandomNumbers(int lower, int upper, int count)
{
    Stack<int> stack = new Stack<int>();
    HashSet<int> voorgekomenGetallen = new HashSet<int>();

    Random randomNumber = new Random();

    while (stack.Count < count)
    {
        int number = randomNumber.Next(lower, upper);
        bool hasOccurred = occurredNumbers.Contains(number);

        while (hasOccurred) {
            number = randomNumber.Next(lower, upper);
            hasOccurred = occurredNumbers.Contains(number);
        }

        stack.Push(number);
        occurredNumbers.Add(number);
    }

    return stack;
}

it cannot find a new number, this is the testcase it fails on: [TestCase(100, 100, 1)]

17 Replies

canton7•5mo ago

Your message says [TestCase(100, 100, 1)], but your image says [TestCase(1, 100, 4)]?

Max•5mo ago

yes, sorry copied the wrong one but it fails on both gets stuck in an infinite loop

canton7•5mo ago

Which of the two loops does it get stuck in?

Max•5mo ago

the hasOccurred loop

canton7•5mo ago

Works here? https://dotnetfiddle.net/djowvV

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canton7•5mo ago

Btw, you can simplify it to:

public static Stack<int> Opdr3RandomNumbers(int lower, int upper, int count)
{
    Stack<int> stack = new Stack<int>();
    HashSet<int> occurredNumbers = new HashSet<int>();

    Random randomNumber = new Random();

    while (stack.Count < count)
    {
        int number = randomNumber.Next(lower, upper);
        if (occurredNumbers.Add(number))
        {
            stack.Push(number);    
        }
    }

    return stack;
}

public static Stack<int> Opdr3RandomNumbers(int lower, int upper, int count)
{
    Stack<int> stack = new Stack<int>();
    HashSet<int> occurredNumbers = new HashSet<int>();

    Random randomNumber = new Random();

    while (stack.Count < count)
    {
        int number = randomNumber.Next(lower, upper);
        if (occurredNumbers.Add(number))
        {
            stack.Push(number);    
        }
    }

    return stack;
}

Or:

public static Stack<int> Opdr3RandomNumbers(int lower, int upper, int count)
{
    Stack<int> stack = new Stack<int>();
    HashSet<int> occurredNumbers = new HashSet<int>();

    Random randomNumber = new Random();

    while (stack.Count < count)
    {
        int number;
        do
        {
            number = randomNumber.Next(lower, upper);
        } while (!occurredNumbers.Add(number));

        stack.Push(number);
    }

    return stack;
}

public static Stack<int> Opdr3RandomNumbers(int lower, int upper, int count)
{
    Stack<int> stack = new Stack<int>();
    HashSet<int> occurredNumbers = new HashSet<int>();

    Random randomNumber = new Random();

    while (stack.Count < count)
    {
        int number;
        do
        {
            number = randomNumber.Next(lower, upper);
        } while (!occurredNumbers.Add(number));

        stack.Push(number);
    }

    return stack;
}

If you ask it for more values than as possible to generate it will get stuck, for sure: Opdr3RandomNumbers(1, 1, 2) will get caught. You probably want some guards to avoid that. Something like Opdr3RandomNumbers(1, 10000, 10000) might take a while to run, as it will need to generate a lot of random numbers before it happens to stumble across the 10000 that it needs

Max•5mo ago

it gets stuck on Opdr3RandomNumbers(10, 15, 6); aswell

canton7•5mo ago

Yep, of course You've said "Give me 6 unique numbers between 10 and 15", and there are only 5 unique numbers between 10 and 15

Max•5mo ago

so if i want to include 10 and 15 i should make the bounds 1 higher and lower?

canton7•5mo ago

With Random.Next, the lower bound is inclusive and the upper is exclusive

canton7•5mo ago

https://learn.microsoft.com/en-us/dotnet/api/system.random.next?view=net-8.0#system-random-next(system-int32-system-int32)

Random.Next Method (System)

Returns a random integer.

Max•5mo ago

Max•5mo ago

this is what i am trying to reproduce

canton7•5mo ago

So if you want the upper bound to be inclusive, you'll need to add 1 to it, yes

Max•5mo ago

okay thank you

canton7•5mo ago

This is how Python's random.sampledoes this FWIW: https://github.com/python/cpython/blob/main/Lib/random.py#L363 That can take what's effectively an ICollection<T> (so something which has a known length, but all items don't need to be listed in advance), and generate a random sample from it

GitHub

cpython/Lib/random.py at main · python/cpython

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Max•5mo ago

thank you, it finally works

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