What is the most efficient way to detect if a string contains a number of consecutive duplicate characters in C#?

Question

For example, a user entered \"I love this post!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!\"

the consecutive duplicate exclamation mark \"!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!\" should b

Answer 1

Here is a quick solution I crafted with some extra duplicates thrown in for good measure. As others pointed out in the comments, some duplicates are going to be completely legitimate, so you may want to narrow your criteria to punctuation instead of mere characters.

string input = "I loove this post!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!aa";

int index = -1;
int count =1;
List dupes = new List();

for (int i = 0; i < input.Length-1; i++)
{
    if (input[i] == input[i + 1])
    {
        if (index == -1)
            index = i;

        count++;
    }
    else if (index > -1)
    {
        dupes.Add(input.Substring(index, count));
        index = -1;
        count = 1;
    }
}

if (index > -1)
{
    dupes.Add(input.Substring(index, count));
}