Strictly following your requirement, everything that is not a letter followed by a space and repeat the sequence until the end of the string
void Main()
{
string test = "P I E T S N O T . C O M";
Console.WriteLine(CheckSpaceLetterSequence(test));
test = "Hi my name is";
Console.WriteLine(CheckSpaceLetterSequence(test));
}
bool CheckSpaceLetterSequence(string test)
{
int count = 0;
bool isSpace = (test[0] == ' ');
for(int x = 1; x < test.ToCharArray().Length; x++)
{
bool curSpace = (test[x] == ' ');
if(curSpace == isSpace)
return false;
isSpace = !isSpace;
count++;
if(count == 3)
break;
}
return true;
}