The function that finds Common Prefix for 2 strings
//converted from http://stackoverflow.com/questions/1250514/find-length-of-initial-segment-matching-mask-on-arrays
public static string LongestCommonPrefix(string str1, string str2)
{
int minLen = Math.Min(str1.Length, str2.Length);
for (int i = 0; i < minLen; i++)
{
if (str1[i] != str2[i])
{
return str1.Substring( 0, i);
}
}
return str1.Substring( 0, minLen);
}