CS2121 lab exercise 1 part a4 - hint
To find all words containing containing exactly one character,
you have to write a pattern that matches the whole line, from start to end.
- At the start of the pattern, match the start of the line,
as in part a3 (hint).
- At the end of the pattern, match the end of the line
- Between the start and end of the pattern, match a single character,
that can be any character