private static Expression Solve(ProblemStatement problem)
{
Queue <Expression> combining = new Queue <Expression>(
problem.InputNumbers.Select(number => new Expression(number)));
List <Expression> known = new List <Expression>();
while (combining.TryDequeue(out Expression current))
{
if (current.Value == problem.DesiredResult)
{
return(current);
}
IEnumerable <Expression> combinableWith = known.Where(
expr => !expr.UsedNumbers.Intersect(current.UsedNumbers).Any()).ToList();
foreach (Expression existing in combinableWith)
{
combining.Enqueue(
current.CombineWith(existing, '+', current.Value + existing.Value));
}
known.Add(current);
}
return(null);
}
static void Main(string[] args)
{
while (true)
{
ProblemStatement problem = ReadProblem();
if (problem == null)
{
break;
}
Expression solution = Solve(problem);
string report = solution?.ToString() ?? "No solution found.";
Console.WriteLine(report);
Console.WriteLine();
}
}