Sometimes what looks simple is complex and what looks complex is simple. See if you can understand how this one calculates all the possible ways to give change for a certain amount of money given some kinds of coins. You MIT guys out there don't count, you probably have read the solution in the same book I have.

BTW: the code works with the LINQ May CTP ...

using System;
using System.Collections.Generic;
using System.Text;
using System.Query;
using System.Xml.XLinq;

class Program
{
    static void Main(string[] args)
    {
        var coins = new int[] { 1, 5, 10, 25, 50 };

        var i = ChangeComb(100, coins);
        Console.WriteLine(i);
    }

    static int ChangeComb(int amount, IEnumerable<int> coins)
    {
        if (amount == 0) return 1;
        if (amount < 0) return 0;
        if (coins.Count() == 0) return 0;

        return ChangeComb(amount, coins.Skip(1)) +
			ChangeComb(amount - coins.First(), coins);
    }
}