Enhancements to "Basic": mainly docs (#211)

* docs(DifferenceArray): specify array argument's eltype as <:Number, fix spelling

* refactor(DifferenceArray): explicitly use `copy` to make a copy

* docs(Basic): add docstring for prefix_sum

* fix(Basic): return array of proper type from prefix_sum instead of Any array

* test(Basic): test prefix_sum on other Number types, not just integers

Author: digital-carver

src/basic/difference_arr.jl

@@ -11,9 +11,12 @@
     - print array after any numbers of changes                - O(N)
 
 # Functions
-    - create_diff_arr(original::Array{T}) - Create difference array for array 'original'
-    - calculate_arr(diff_arr::Array{T}) - Create a original array from the given difference array
-    - add_to_arr(diff_arr::Array{T}, l::Int, r::Int, x::Number) - Add x to all elements with index from [l, r]
+    - create_diff_arr(original::Array{<:Number})
+        * Create difference array for array 'original'
+    - calculate_arr(diff_arr::Array{<:Number})
+        * Recreate the original array from the given difference array
+    - add_to_arr(diff_arr::Array{<:Number}, l::Int, r::Int, x::Number)
+        * Add x to all elements with index from [l, r]
 
 
 # Contributed by: [Nikola Mircic](https://github.com/Nikola-Mircic)
@@ -25,7 +28,7 @@ module DifferenceArray
 function create_diff_arr(original::Array{T}) where {T<:Number}
     n = length(original)
 
-    diff_arr = Array(original)
+    diff_arr = copy(original)
 
     for i in 2:n
         diff_arr[i] = original[i] - original[i-1]
@@ -40,7 +43,7 @@ end
 function calculate_arr(diff_arr::Array{T}) where {T<:Number}
     n = length(diff_arr)
 
-    arr = Array(diff_arr)
+    arr = copy(diff_arr)
 
     for i in 2:n
         arr[i] = diff_arr[i] + arr[i-1]
@@ -51,7 +54,7 @@ end
 
 # Add x to all elements with index from [l, r]
 # Parameters:
-#   - dif_arr - a difference array of the array you want to change
+#   - diff_arr - a difference array of the array you want to change
 #   - l - leftmost index of the affected range
 #   - r - rightmost index of the affected range
 #   - x - a value to be added to all elements from a given range

src/basic/prefix_sum.jl

@@ -1,5 +1,32 @@
+"""
+    prefix_sum(arr::Vector{<:Number})
+
+# Brief
+Given an input array of numbers, return an array of the sum of each "prefix" of the input array i.e.
+the 1st element, 1st + 2nd element, 1st + 2nd + 3rd, etc.
+
+This functionality is available in base Julia as `cumsum`.
+
+# Arguments
+- `arr`: an array of numbers
+
+# Examples
+```julia
+julia> prefix_sum([1, 2, 3])
+3-element Vector{Int64}:
+ 1
+ 3
+ 6
+
+julia> prefix_sum([0.0, 10.0, π])
+3-element Vector{Float64}:
+  0.0
+ 10.0
+ 13.141592653589793
+```
+"""
 function prefix_sum(arr::Vector{T}) where {T<:Number}
-    pre = []
+    pre = T[]
     preans = zero(T)
     for i in arr
         preans += i

test/basic.jl

@@ -4,6 +4,9 @@ using TheAlgorithms.Basic
     @testset "Basic: prefix_sum" begin
         @test Basic.prefix_sum([1, 1, 1]) == [1, 2, 3]
         @test Basic.prefix_sum([1, 2, 3]) == [1, 3, 6]
+        @test Basic.prefix_sum(BigInt[]) == BigInt[]
+        @test Basic.prefix_sum([0., 0., 0.]) == [0., 0., 0.]
+        @test Basic.prefix_sum([1 + 2im, 2 - 3im]) == [1 + 2im, 3 - 1im]
     end
 
     @testset "Basic: DifferenceArray" begin