N queens math (#2175)

* add new file for another solution to the n queens problem

* Add the code for the algorithm, add comments and add at the top a general explanation

* Update backtracking/n_queens_math.py

Co-authored-by: Christian Clauss <cclauss@me.com>

* Update backtracking/n_queens_math.py

Co-authored-by: Christian Clauss <cclauss@me.com>

* Update backtracking/n_queens_math.py

Co-authored-by: Christian Clauss <cclauss@me.com>

* Update backtracking/n_queens_math.py

Co-authored-by: Christian Clauss <cclauss@me.com>

* No newline at the end of the file

* Type hints

* whitespaces fixed

* Fixed whitespaces

* Add type hints

* CodeSpell fixed

* update

* All changes made except changing the board variable to local

* Add doctest

* Update

* Update

* Update

* Update n_queens_math.py

Co-authored-by: Christian Clauss <cclauss@me.com>