Question

The messages are exact dont need to worry about variation or simbols in between, right now I am just looking for a efficient way that can check messages like the below.

I have a message like:

string msg = "This is a small message !";

And I would like to check if that message was sent repeated times in the same string like this:

string msg = "This is a small message !This is a small message !";

or:

string msg = "This is a small message !This is a small message !This is a small message !";

or:

string msg = "This is a small message !This is a small message !This is a small message !This is a small message !This is a small message !";

I have a LinkedList<string> that stores the last 3 messages received and along with those last 3 message I would like to match the current messages to see if it is either equal to one of the current store messages or a repetition of any.

foreach (string item in myListOfMessages)
{
    if (string.Equals(msg, item))
    {
        // the message matchs one of the stored messages
    }
    else if (msg.Lenght == (item.Lenght * 2) && string.Equals(msg, string.Concat(item, "", item)))
    {
        // the message is a repetition, and ofc only works when some one sends the message twice in the same string
    }
}

Like I showed in the examples, the repetition could be quite large, also I am not sure if the method I presented above is the best one for what I need. It was the first idea that came to my mind but soon after I realised that it would produce a lot more work that way.

Answer 1

Linq to the rescue:

string msg = "This is a small message !";
string otherMsg = "This is a small message !This is a small message !This is a small message !This is a small message !This is a small message !";

bool isRepeated = Enumerable.Range(0, otherMsg.Length / msg.Length)
                            .Select(i => otherMsg.Substring(i *  msg.Length,  msg.Length))
                            .All( x => x == msg);

This approach basically takes a sub string of the length of the first message and compares each chunk with the original message.

Wrapped in a method with some pre-checking:

public bool IsRepeated(string msg, string otherMsg)
{
    if (otherMsg.Length < msg.Length || otherMsg.Length % msg.Length != 0)
        return false;

    bool isRepeated = Enumerable.Range(0, otherMsg.Length / msg.Length)
                                .Select(i => otherMsg.Substring(i * msg.Length, msg.Length))
                                .All(x => x == msg);
    return isRepeated;
}

Edit:

Above approach will generate unnecessary strings that will have to be gc’ed – a much more efficient and faster solution:

public bool IsRepeated(string msg, string otherMsg)
{
    if (otherMsg.Length < msg.Length || otherMsg.Length % msg.Length != 0)
        return false;

    for (int i = 0; i < otherMsg.Length; i++)
    {
        if (otherMsg[i] != msg[i % msg.Length])
            return false;
    }
    return true;
}