find number of repeating substrings in a string

The solution for this with C# is:

 class Program
 {
     public static string CountOfRepeatedSubstring(string str)
     {
         if (str.Length < 2)
         {
             return "-1";
         }

         StringBuilder substr = new StringBuilder();

         // Length of the substring cannot be greater than half of the actual string
         for (int i = 0; i < str.Length / 2; i++)
         {
             // We will iterate through half of the actual string and
             // create a new string by appending the current character to the previous character
             substr.Append(str[i]);

             String clearedOfNewSubstrings = str.Replace(substr.ToString(), "");

             // We will remove the newly created substring from the actual string and 
             // check if the length of the actual string, cleared of the newly created substring, is 0.
             // If 0 it tells us that it is only made of its substring
             if (clearedOfNewSubstrings.Length == 0)
             {
                 // Next we will return the count of the newly created substring in the actual string.
                 var countOccurences = Regex.Matches(str, substr.ToString()).Count;

                 return countOccurences.ToString();
             }
         }

         return "-1";
     }       

     static void Main(string[] args)
     {
         // Input: {"abcdaabcdaabcda"}
         // Output: 3

         // Input: { "abcdaabcdaabcda" }
         // Output: -1

         // Input: {"barrybarrybarry"}
         // Output: 3            

         var s = "asdf"; // Output will be -1

         Console.WriteLine(CountOfRepeatedSubstring(s));
     }
 }

How do you want to specify the "repeating string"? Is it simply the first group of characters up until either a) the first character is found again, b) the pattern begins to repeat, or c) some other criteria?

So, if your string is "ABBAABBA", is that a 2 because "ABBA" repeats twice or is it 1 because you have "ABB" followed by "AAB"? What about "ABCDABCE" -- does "ABC" count (despite the "D" in between repetitions?) In "ABCDABCABCDABC", is the repeating string "ABCD" (1) or "ABCDABC" (2)?

What about "AAABBAAABB" -- is that 3 ("AAA") or 2 ("AAABB")?

If the end of the repeating string is another instance of the first letter, it's pretty simple:

Work your way through the string character by character, putting each character into another variable as you go, until the next character matches the first one. Then, given the length of the substring in your second variable, check the next bit of your string to see if it matches. Continue until it doesn't match or you hit the end of the string.

If you just want to find any length pattern that repeats regardless of whether the first character is repeated within the pattern, it gets more complicated (but, fortunately, it's the sort of thing computers are good at).

You'll need to go character by character building a pattern in another variable as above, but you'll also have to watch for the first character to reappear and start building a second substring as you go, to see if it matches the first. This should probably go in an array as you might encounter a third (or more) instance of the first character which would trigger the need to track yet another possible match.

It's not difficult but there is a lot to keep track of and it's a rather annoying problem. Is there a particular reason you're doing this?