[Project Euler] Fix code style for multiple problems (#3094)

* Fix code style for Project Euler problems:

- 13, 17, 21
- Default args
- Type hints
- File path

* Fix code style for multiple problems

* Made suggested changes

Dhruv committed 5y ago

501a2ff430c403570f992f0e1017d81b0638b2ef

Parent: c961d55

Committed by GitHub <noreply@github.com> on 10/10/2020, 3:53:17 PM