factorial of n numbers using c# lambda..?

Question

I just started playing with lambdas and Linq expression for self learning. I took the simple factorial problem for this. with the little complex scenario where find the fact

Answer 1

Just to continue on Jon's answer, here's how you can memoize the factorial function so that you don't recompute everything at each step :

public Func Memoize(Func func)
{
    Dictionary _resultsCache = new Dictionary();
 return (arg) =>
 {
     TResult result;
     if (!_resultsCache.TryGetValue(arg, out result))
  {
   result = func(arg);
   _resultsCache.Add(arg, result);
  }
  return result;
 };
}

...

Func factorial = null; // Just so we can refer to it
factorial = x => x <= 1 ? 1 : x * factorial(x-1);
var factorialMemoized = Memoize(factorial);
var res = Enumerable.Range(1, 10).Select(x => factorialMemoized(x));
foreach (var outt in res)
    Console.WriteLine(outt.ToString());

EDIT: actually the code above is not correct, because factorial calls factorial, not factorialMemoized. Here's a better version :

Func factorial = null; // Just so we can refer to it
Func factorialMemoized = null;
factorial = x => x <= 1 ? 1 : x * factorialMemoized(x-1);
factorialMemoized = Memoize(factorial);
var res = Enumerable.Range(1, 10).Select(x => factorialMemoized(x));
foreach (var outt in res)
    Console.WriteLine(outt.ToString());

With that code, factorial is called 10 times, against 55 times for the previous version