Question

Consider we have these three lists:

    List<string> l1= new List<string>(){"A","B","C"};
    List<string> l2= new List<string>(){"A","C","B"};

    List<string> l3= new List<string>(){"B","C"};

I need LINQ query which say l1 includes l3 but l2 doesn’t.

Answer 1

To respect the order and account for possible duplicate elements you have to enumerate the sequence, one way of doing it would be to check for each start position in the source enumeration if the other sequence starts here, e.g. using an extension method:

public static bool ContainsSequence<T>(this IEnumerable<T> source, 
                                       IEnumerable<T> other)
{
    int count = other.Count();

    while (source.Any())
    {
        if (source.Take(count).SequenceEqual(other))
            return true;
        source = source.Skip(1);
    }
    return false;
}

Note that this would be O(n²) since worst case you have fully enumerate the other enumeration for each item in the source collection.

Now you can do:

List<string> l1 = new List<string>() { "A", "B", "C" };
List<string> l2 = new List<string>() { "A", "C", "B" };
List<string> l3 = new List<string>() { "B", "C" };

bool l1ContainsL2 = l1.ContainsSequence(l2); //returns false
bool l1ContainsL3 = l1.ContainsSequence(l3); //returns true