Struct FenwickTree 

pub struct FenwickTree { /* private fields */ }

A Fenwick tree (Binary Indexed Tree) for prefix sums.

Implementations

impl FenwickTree

pub fn new(n: usize) -> Self

Create a FenwickTree of size n (all zeros).

pub fn update(&mut self, i: usize, delta: i64)

Add delta to position i (1-indexed).

pub fn query(&self, i: usize) -> i64

Compute prefix sum [1..=i].

pub fn len(&self) -> usize

Return the size.

pub fn is_empty(&self) -> bool

Return true if empty.