Find Nth occurrence of a character in a string

I need help with creating a C# method that returns the index of the Nth occurrence of a character in a string.

For instance, the 3rd occurrence of the character 't' in the string "dtststxtu" is 5.
(Note that the string has 4 ts.)

Solution 1:

public int GetNthIndex(string s, char t, int n)
{
    int count = 0;
    for (int i = 0; i < s.Length; i++)
    {
        if (s[i] == t)
        {
            count++;
            if (count == n)
            {
                return i;
            }
        }
    }
    return -1;
}

That could be made a lot cleaner, and there are no checks on the input.

Solution 2:

There is a minor bug in previous solution.

Here is some updated code:

s.TakeWhile(c => (n -= (c == t ? 1 : 0)) > 0).Count();

Solution 3:

Here's another LINQ solution:

string input = "dtststx";
char searchChar = 't';
int occurrencePosition = 3; // third occurrence of the char
var result = input.Select((c, i) => new { Char = c, Index = i })
                  .Where(item => item.Char == searchChar)
                  .Skip(occurrencePosition - 1)
                  .FirstOrDefault();

if (result != null)
{
    Console.WriteLine("Position {0} of '{1}' occurs at index: {2}",
                        occurrencePosition, searchChar, result.Index);
}
else
{
    Console.WriteLine("Position {0} of '{1}' not found!",
                        occurrencePosition, searchChar);
}

Just for fun, here's a Regex solution. I saw some people initially used Regex to count, but when the question changed no updates were made. Here is how it can be done with Regex - again, just for fun. The traditional approach is best for simplicity.

string input = "dtststx";
char searchChar = 't';
int occurrencePosition = 3; // third occurrence of the char

Match match = Regex.Matches(input, Regex.Escape(searchChar.ToString()))
                   .Cast<Match>()
                   .Skip(occurrencePosition - 1)
                   .FirstOrDefault();

if (match != null)
    Console.WriteLine("Index: " + match.Index);
else
    Console.WriteLine("Match not found!");