Please include explanation as this is slightly different than questions already posted

A run in a string is a substring of length at least two, as long as possible and consisting entirely of the same symbol. For instance, the string abbbaab contains a run of b 's of length three and a run of a 's of length two. Find dfa's for the following languages on {a,b}. (a) L={w:w contains no runs of length less than three }. (b) L={w : every run of a 's has length either two or three }