C# algorithm - find least number of objects necessary

Question

Let\'s say I have the following code.

var numberToGetTo = 60; 
var list = new[] {10, 20, 30, 40, 50};

I want to be able to return 50 &

Answer 1

Here's an implementation that uses Linq to be as clean as possible. It makes no attempt to optimize for performance over large inputs.

I'm assuming that you wouldn't use this algorithm for large inputs anyway, since the problem is NP-Complete, and therefore clarity is the right goal. My algorithm is O(n^2), and recursive at that.

    static IEnumerable Knapsack(IEnumerable items, int goal)
    {
        var matches = from i in items
                      where i <= goal
                      let ia = new[] {i}
                      select i == goal ? ia : Knapsack(items, goal - i).Concat(ia);

        return matches.OrderBy(x => x.Count()).First();
    }