Given the alphabet, Σ= {c d}, give the regular expression that defines the language consisting of all string that have exactly one triple letter in them. Although this question is straight-forward, there are a lot of cases and the solution is reasonably complex. You'll make great progress by considering the fact that ddcdcccdcd is valid word in this language.
Here is my answer (wondering if I am on the right page or not?):
d*c*(ccc) + (ddd) d*c*d*