* Enhance fenwick_tree.py
* Change update to add in fenwick_tree.py
* Some changes
* Fix bug
* Add O(N) initializer to FenwickTree
* Add get method to Fenwick Tree
* Change tree in Fenwick Tree
* Add rank query to FenwickTree
* Add get_array method to FenwickTree
* Add some tests
* Update data_structures/binary_tree/fenwick_tree.py
Co-authored-by: Christian Clauss <cclauss@me.com>
* Update data_structures/binary_tree/fenwick_tree.py
Co-authored-by: Christian Clauss <cclauss@me.com>
* Update data_structures/binary_tree/fenwick_tree.py
Co-authored-by: Christian Clauss <cclauss@me.com>
* change `List` to `list`
Co-authored-by: Christian Clauss <cclauss@me.com>