How to check if list contains another list in same order

Question

Is there any simple way in c# to check if list consist of another list?. Here is example, I have:

var list1 = new List<int>() {1, 2, 3, 4, 5, 6,}; and second one var list2 = new List<int>() {5, 6};

this list is a part of first list so it should return true.

var list1 = new List<int>() {1, 2, 3, 4, 5, 6,}; and var list3 = new List<int>() {1, 3}; should return false.

It's not about checking if all elements in first list exist in second list but also about order. It has to have the same order.

Answer 1

This works for me:

public bool ContainsSubsequence<T>(List<T> sequence, List<T> subsequence)
{
    return
        Enumerable
            .Range(0, sequence.Count - subsequence.Count + 1)
            .Any(n => sequence.Skip(n).Take(subsequence.Count).SequenceEqual(subsequence));
}

This code uses Enumerable.Range to run through every possible starting point within sequence that could be the same as subsequence , and checks if the segment of sequence the same size as subsequence at this position is actually equal to subsequence .

So for this code:

var list1 = new List<int>() { 1, 2, 3, 4, 5, 6, };
var list2 = new List<int>() { 5, 6, };
var list3 = new List<int>() { 1, 3, };

Console.WriteLine(ContainsSubsequence(list1, list2));
Console.WriteLine(ContainsSubsequence(list1, list3));

I get:

True
False

Answer 2

Thanks @GeorgeVovos & @Enigmativity for pointing out the issues in first solution.

public static bool HasSubSequence(List<int> main, List<int> query)
{
    var startIndex = main.IndexOf(query.First());
    if (main == null || query == null || startIndex < 0)
        return false;

    while (startIndex >= 0)
    {        
        if (main.Count - startIndex < query.Count)
            return false;
        var nonMatch = false;
        for (int i = 0; i < query.Count; i++)
        {
            if (main[i + startIndex] != query[i])
            {
                main = main.Skip(startIndex + 1).ToList();
                startIndex = main.IndexOf(query.First());
                nonMatch = true;
                break;
            }
        }
        if (!nonMatch)
            return true;
    }
    return false;
}

Example

var l1 = new List<int> { 1, 2, 3, 4, 5 };
var l2 = new List<int> { 4, 5 };
var l3 = new List<int> { 1, 3 };
var l4 = new List<int> { 5, 6 };

var l5 = new List<int> { 1, 2, 3, 2, 5, 6, 2, 4, 8 };
var l6 = new List<int> { 2, 4 };

var test1 = HasSubSequence(l1, l2); //true
var test2 = HasSubSequence(l1, l3); //false
var test3 = HasSubSequence(l1, l4); //false

var test5 = HasSubSequence(l5, l6); //true