Add documentation for FenwickTree (#492)

Add documentation for FenwickTree

README.md

@@ -28,6 +28,7 @@ This package implements a variety of data structures, including
 -   Sorted Dict, Sorted Multi-Dict and Sorted Set
 -   DataStructures.IntSet
 -   Priority Queue
+-   Fenwick Tree
 
 Resources
 ---------

docs/make.jl

@@ -12,6 +12,7 @@ makedocs(
         "circ_deque.md",
         "stack_and_queue.md",
         "priority-queue.md",
+        "fenwick.md",
         "accumulators.md",
         "disjoint_sets.md",
         "heaps.md",

docs/src/fenwick.md

@@ -0,0 +1,25 @@
+# Fenwick Tree
+
+The `FenwickTree` type is data structures which is used for handling increment and decrement to prefix-sums of an array efficiently.
+
+Usage:
+
+```julia
+FenwickTree{T}(n) # Constructs a Fenwick Tree of length `n`
+FenwickTree{T}(counts)  # Constructs a Fenwick Tree from an array of `counts`
+inc!(ft, ind, val)  # Increases the value of the FenwickTree `ft` by `val` from the index `ind` upto the length of `ft`
+dec!(ft, ind, val)  # Decreases the value of the FenwickTree `ft` by `val` from the index `ind` upto the length of `ft`
+incdec!(ft, left, right, val)  # Increases the value of the FenwickTree `ft` by `val` from the indices from `left` and decreases it from the `right`
+prefixsum(ft, ind)  # Return the cumulative sum from index 1 upto `ind` of the FenwickTree `ft`
+```
+
+Examples:
+
+```julia
+julia> f = FenwickTree{Int}(6)
+julia> inc!(f, 2, 5)
+julia> prefixsum(f, 1)
+ 0
+julia> prefixsum(f, 3)
+ 5
+```

src/fenwick.jl

@@ -1,18 +1,18 @@
+struct FenwickTree{T}
+    bi_tree::Vector{T} #bi_tree is shorthand for Binary Indexed Tree, an alternative name for Fenwick Tree
+    n::Int
+end
+
 """
     FenwickTree{T}(n)
     
 Constructs a [`FenwickTree`](https://en.wikipedia.org/wiki/Fenwick_tree) of length `n`.
  
 """
-struct FenwickTree{T}
-    bi_tree::Vector{T} #bi_tree is shorthand for Binary Indexed Tree, an alternative name for Fenwick Tree
-    n::Int
-end
-
 FenwickTree{T}(n::Integer) where T = FenwickTree{T}(zeros(T, n), n)
 
 """
-    FenwickTree(arr::AbstractArray) 
+    FenwickTree(counts::AbstractArray) 
     
 Constructs a [`FenwickTree`](https://en.wikipedia.org/wiki/Fenwick_tree) from an array of `counts`