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Program.cs
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Program.cs
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// See https://aka.ms/new-console-template for more information
int[]? numbers = null;
int targetNumber = int.MinValue;
Console.WriteLine("NOTE: Performs at O(n!) according to available numbers.");
while (numbers == null)
{
Console.WriteLine("Enter the available numbers (comma separated):");
string[]? numbersInput = Console.ReadLine()?.Split(',', StringSplitOptions.RemoveEmptyEntries);
if (numbersInput != null && numbersInput.All(numberInput => int.TryParse(numberInput.Trim(), out int _)))
{
numbers = numbersInput.Select(numberInput => int.Parse(numberInput.Trim())).ToArray();
Console.WriteLine("You entered: " + string.Join(", ", numbers));
if (numbers.Length > 6)
{
Console.WriteLine("WARNING: This may take a while... Continue (y/n)?");
ConsoleKey input;
while ((input = Console.ReadKey().Key) is not (ConsoleKey.Y or ConsoleKey.N)) { /* Wait for valid input */ }
if (input == ConsoleKey.N)
{
numbers = null;
}
Console.WriteLine();
}
}
else
{
Console.WriteLine("Invalid input. Please try again.");
}
}
while (targetNumber == int.MinValue)
{
Console.WriteLine("Enter the target number:");
string? numberInput = Console.ReadLine();
if (int.TryParse(numberInput, out int number))
{
targetNumber = number;
Console.WriteLine("You entered: " + targetNumber);
}
else
{
Console.WriteLine("Invalid input. Please try again.");
}
}
Console.WriteLine("Off we go...");
await FindResults(numbers, targetNumber);
Console.WriteLine("Done!");
async Task FindResults(int[]? numbers, int targetNumber)
{
if (numbers == null)
{
return;
}
var workingNumbers = numbers.Select(number => new WorkingNumber { Number = number, Source = number.ToString() }).ToArray();
var results = await DeriveNextWorkingNumbers(targetNumber, workingNumbers);
foreach (var result in results.Distinct())
{
Console.WriteLine($"{result.Number} = {result.Source}");
}
}
async Task<IEnumerable<WorkingNumber>> DeriveNextWorkingNumbers(int targetNumber, WorkingNumber[] workingNumbers)
{
// Check up front if we have an answer.
var result = workingNumbers.Where(wn => wn.Number == targetNumber);
if (result.Any())
{
return result;
}
else if (workingNumbers.Length == 1)
{
// We have no answer and no more numbers to work with.
return Enumerable.Empty<WorkingNumber>();
}
// Work through the set, grabbing two numbers at a time to derive a composite number,
// and work on that composite number that with the rest of the set.
var waitResult = await Task.WhenAll(workingNumbers.Select(async (workingNumber, index1) =>
{
var localResult = Enumerable.Empty<WorkingNumber>();
for (int index2 = 0; index2 < workingNumbers.Length; index2++)
{
if (index2 == index1)
{
// Same working number. Skip.
continue;
}
var otherWorkingNumber = workingNumbers[index2];
var nextSet = workingNumbers.Where((wn, index3) => index3 != index1 && index3 != index2).ToArray();
localResult = localResult.Concat(await DeriveNextWorkingNumbers(targetNumber, nextSet
.Concat(new[] { new WorkingNumber
{
Number = workingNumber.Number + otherWorkingNumber.Number,
Source = $"({workingNumber.Source} + {otherWorkingNumber.Source})"
} }).ToArray()));
localResult = localResult.Concat(await DeriveNextWorkingNumbers(targetNumber, nextSet
.Concat(new[] { new WorkingNumber
{
Number = workingNumber.Number - otherWorkingNumber.Number,
Source = $"({workingNumber.Source} - {otherWorkingNumber.Source})"
} }).ToArray()));
localResult = localResult.Concat(await DeriveNextWorkingNumbers(targetNumber, nextSet
.Concat(new[] { new WorkingNumber
{
Number = workingNumber.Number * otherWorkingNumber.Number,
Source = $"({workingNumber.Source} * {otherWorkingNumber.Source})"
} }).ToArray()));
// Check division only if result is valid and an integer.
if (otherWorkingNumber.Number != 0 && workingNumber.Number % otherWorkingNumber.Number == 0)
{
localResult = localResult.Concat(await DeriveNextWorkingNumbers(targetNumber, nextSet
.Concat(new[] { new WorkingNumber
{
Number = workingNumber.Number / otherWorkingNumber.Number,
Source = $"({workingNumber.Source} / {otherWorkingNumber.Source})"
} }).ToArray()));
}
// Check power only if exponent is valid and small.
if ((otherWorkingNumber.Number is >= 0 and <= 4) && Math.Abs(workingNumber.Number) < (2048 >> otherWorkingNumber.Number))
{
localResult = localResult.Concat(await DeriveNextWorkingNumbers(targetNumber, nextSet
.Concat(new[] { new WorkingNumber
{
Number = (int)Math.Pow(workingNumber.Number, otherWorkingNumber.Number),
Source = $"({workingNumber.Source} ^ {otherWorkingNumber.Source})"
} }).ToArray()));
}
}
return localResult;
}));
return waitResult.SelectMany(r => r);
}