C# - Optimizing finding elements in a list by comparing with array

Question

I have a list containing some objects and an string array. I would like to optimize this code if possible. Currently, the Big O notation is O(n^2)

The simplified version of the code:

        List<Client> clients = new List<Client>();
        // ... fill the 'clients' list

        string[] ids = File.ReadAllLines("ids.txt");

        List<Client> result = new List<Client>();
        for (int i = 0; i < ids.Length; i++)
        {
            foreach (var item in clients)
            {
                if (clients.Id == ids[i])
                {
                    result.Add(item);
                    break;
                }
            }
        }

        return result;

Create a hashset from ids.

Maxim Tkachenko
– Maxim Tkachenko

2022-05-10 09:25:05 +00:00
Commented May 10, 2022 at 9:25 — Maxim Tkachenko
– Maxim Tkachenko, Commented May 10, 2022 at 9:25
Do you have a typo? Is it clients.Id or item.Id?

Nikola Develops
– Nikola Develops

2022-05-10 09:28:01 +00:00
Commented May 10, 2022 at 9:28 — Nikola Develops
– Nikola Develops, Commented May 10, 2022 at 9:28

Eli Blokh · Accepted Answer · 2022-05-10 09:28:54Z

4

You can use Dictionary

Dictionary<string, Client> clients = new Dictionary<string, Client>();

Use the client's id as a key

Then, just go through the id array in one loop and retrieve clients.

answered May 10, 2022 at 9:28

Eli Blokh

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Comments

Nikola Develops · Accepted Answer · 2022-05-10 09:33:33Z

0

You can use LINQ like this:

    string[] ids = File.ReadAllLines("ids.txt");

    List<Client> result = clients.Where(x => ids.Contains(x.Id)).ToList();

    return result;

answered May 10, 2022 at 9:33

Nikola Develops

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