C＃比较两个有序列表以获取更新的值

Question

I have a data source containing say, 6 items, order important, which updates each time I check it.
Here is the initial list
List 1:

• dog
• cat
• fish
• cat
• cat
• mouse

I then wait, the list updates some amount with the top items being removed and new ones added. Here is the new list I fetch.
List 2:

• fish
• cat
• cat
• mouse
• cat
• hamster

I would like a way of finding out the new values which were added, cat + hamster in this case.

My actual problem has a source of 38 items and each check, between 0 - 38 items have been added to the bottom. I cannot view any more than the latest 38 items however.

Example

        List<string> list1 = new List<string>();
        List<string> list2 = new List<string>();

        list1.Add("dog");
        list1.Add("cat");
        list1.Add("fish");
        list1.Add("cat");
        list1.Add("cat");
        list1.Add("mouse");

        list2.Add("fish");
        list2.Add("cat");
        list2.Add("cat");
        list2.Add("mouse");
        list2.Add("cat");
        list2.Add("hamster");

        Console.WriteLine("List 1" + Environment.NewLine);

        foreach(string item in list1)
        {
            Console.WriteLine(item);
        }

        Console.WriteLine(Environment.NewLine + "List 2" + Environment.NewLine);

        foreach (string item in list2)
        {
            Console.WriteLine(item);
        }

        var newItems = list2.Except(list1);

        Console.WriteLine(Environment.NewLine + "New Items" + Environment.NewLine);

        foreach (string item in newItems)
        {
            Console.WriteLine(item);
        }

Using Except, the result is 'hamster' as cat did exist in the first list and except does not seem to check order (Is there a way?)

Now, this seems easy and like it should have been answered so I presume I'm just not typing the right thing into search.

Any help appreciated.

EDIT I can imagine a solution by looping through lists of increasing size, starting with the last value of list 1 and the first value of list 2 and then using SequenceEqual() until false to count how many items overlap and going from there. Would this be a good solution?

Solution Used I did as mentioned in my edit and looped through comparing lists of increasing size for a match using SequenceEqual()

Im sure this is inefficient but this wont pose as issue for me. If anyone does know a neater trick, that would be great.

        int size1 = list1.Count();
        int size2 = list2.Count();

        int i;
        for (i = 1; i <= size2; i++)
        {
            List<string> aList = list1.GetRange(size1 - i, i);
            List<string> bList = list2.GetRange(0, i);
            if(aList.SequenceEqual(bList))
            {
                break;
            }
        }

        int totalAdded = size2 - i;
        List<string> newItemsList = list2.GetRange(i, totalAdded);

        foreach (string item in newItemsList)
        {
            Console.WriteLine(item);
        }

        Console.ReadLine();

Answer 1

If I understand you correctly, you are looking to create a third list with the new items? Or at least find the new items:

List<string> newItems = new List<string>();
newItems.AddRange(list2.FindAll(s=> !list1.Contains(s)));

Answer 2

The issue that StriplingWarrior mentioned in the comment is very important. Although its possibility is low, but the solution should be the one that works in all cases.

I recommend you to change your data structure and add an integer next to your entities. The integer is called ID or Key which shows the difference between cat with ID = 3 and cat with ID = 7. so you will never get confused about which cat you are looking for.

The best structure for the new structure is called Dictionary .

I changed your code below, which results cat and hamster :

        int incrementalID = 0;
        Dictionary<int, string> list1 = new Dictionary<int, string>();
        Dictionary<int, string> list2 = new Dictionary<int, string>();

        list1.Add(incrementalID++, "dog");    //ID = 0
        list1.Add(incrementalID++, "cat");     //ID = 1
        list1.Add(incrementalID++, "fish");    //ID = 2
        list1.Add(incrementalID++, "cat");     //ID = 3
        list1.Add(incrementalID++, "cat");     //ID = 4
        list1.Add(incrementalID++, "mouse");   //ID = 5

        list2 = new Dictionary<int, string>(list1);
        list2.Remove(0);
        list2.Remove(1);
        list2.Add(incrementalID++, "cat");      //ID = 6
        list2.Add(incrementalID++, "hamster");  //ID = 7;

        Console.WriteLine("List 1" + Environment.NewLine);

        foreach (string item in list1.Values)
        {
            Console.WriteLine(item);
        }

        Console.WriteLine(Environment.NewLine + "List 2" + Environment.NewLine);

        foreach (string item in list2.Values)
        {
            Console.WriteLine(item);
        }

        var newItems = list2.Except(list1);

        Console.WriteLine(Environment.NewLine + "New Items" + Environment.NewLine);

        foreach (KeyValuePair<int, string> item in newItems)
        {
            Console.WriteLine(item.Value);
        }