Recursive Algorithm C#

Question

I need some help with an algorithm using C#. I have a list of objects, with items multiples of 4, and I should return only the two best items. Each item has a value and a description. I must also make comparisons to every two elements. And I would like to call this method recursively until I have only 2 elements.

Example:

CardList.Add(new Card("Name A", 150));
CardList.Add(new Card("Name B", 100));
CardList.Add(new Card("Name C", 50));
CardList.Add(new Card("Name D", 556));
CardList.Add(new Card("Name E", 170));
CardList.Add(new Card("Name F", 160));
CardList.Add(new Card("Name G", 30));
CardList.Add(new Card("Name H", 650));


public Lis<Card> BestCards(Lis<Card> list){
    List<Card> listResult = new List<Card>(); 
    for(int i=1; i<=list.lenght; i+2)
    {
        if(list[i].value> list[i+1].value)
            listResult.Add(list[i])
        else if (list[i].value< list[i+1].value)
            listResult.Add(list[i+1])
        else if (list[i].value==list[i+1].value)    
        {
            // first element according to alphabetical order of the description
            listResult.Add(???)
        }   
    return listResult;
}

Any suggestion?

Answer 1

Using the method that you are currently using, you could be losing data, since you are getting rid of an item every time you do a comparison, without checking if it is better than the whole list.

I would suggest sorting the list, and then taking the top two items that way, or you can compare one item to every other item, and find the best two.

Answer 2

This solution should meet your requirements.

The first method iterates while there are more than 2 cards remaining, the second method compares the cards and returns the resulting list:

public List<Card> BestCards(List<Card> list){
    List<Card> listResult = list; 

    while (listResult.Count > 2)
        listResult = ReduceList(listResult);

    return listResult;
}


public List<Card> ReduceList(List<Card> list)
{
    var listResult = new List<Card>(); 

    for(int i = 0; i <= list.Count - 1; i+=2)
    {
        if(list[i].value > list[i+1].value)
            listResult.Add(list[i]);
        else if (list[i].value< list[i+1].value)
            listResult.Add(list[i+1]);
        else if (list[i].value==list[i+1].value)
            listResult.Add(list[i].name.CompareTo(list[i+1].name) <= 0 ? list[i] : list[i+1]);
    }

    return listResult;
}