Crate fenwick 

Fenwick Tree (Binary Indexed Tree)

Fenwick Tree is a data structure that can efficiently update elements and calculate prefix sums in a table of numbers.

Given an array of n numbers, the prefix sum up to index i is the sum of the first i elements. Fenwick Tree supports both update and prefix-sum queries in O(log n) time by storing partial sums in a tree whose node ranges are determined by the least significant bit of each index.

Structs

FenwickTree

Fenwick Tree (Binary Indexed Tree).