factorial iterative & recursive (TheAlgorithms#39)

src/TheAlgorithms.jl

@@ -32,6 +32,8 @@ export area_triangle
 export ceil_val, floor_val
 export collatz_sequence
 export euler_method
+export factorial_iterative
+export factorial_recursive
 export is_armstrong
 export line_length
 export mean
@@ -86,6 +88,7 @@ include("math/average_mode.jl")
 include("math/ceil_floor.jl")
 include("math/collatz_sequence.jl")
 include("math/euler_method.jl")
+include("math/factorial.jl")
 include("math/line_length.jl")
 include("math/perfect_cube.jl")
 include("math/perfect_number.jl")

src/math/factorial.jl

@@ -0,0 +1,52 @@
+"""
+    factorial_iterative(n)
+
+Finds factorial of a number using Iterative method
+
+# Example
+```julia
+factorial_iterative(5)      # returns 120
+factorial_iterative(0.1)    # returns error
+factorial_iterative(-1)     # returns error
+```
+# Reference
+- factorial of a positive integer -- https://en.wikipedia.org/wiki/Factorial
+
+Contributed By:- [Ashwani Rathee](https://github.com/ashwani-rathee)
+"""
+function factorial_iterative(n)
+    if n != trunc(n) || n < 0
+        throw(error("factorial_iterative() only accepts non-negative integral values"))
+    end
+    factorial::BigInt = 1
+    map(i -> factorial *= i, 1:n)
+    return factorial
+end
+
+"""
+    factorial_recursive(n)
+
+Finds factorial of anumber using recursive method
+
+# Example
+```julia
+factorial_recursive(5)      # returns 120
+factorial_recursive(0.1)    # returns error
+factorial_recursive(-1)     # returns error
+```
+# Reference
+- factorial of a positive integer -- https://en.wikipedia.org/wiki/Factorial
+
+Contributed By:- [Ashwani Rathee](https://github.com/ashwani-rathee)
+"""
+function factorial_recursive(n)
+    if n != trunc(n) || n < 0
+        throw(error("factorial_iterative() only accepts non-negative integral values"))
+    end
+    if n == 0 || n == 1
+        return 1
+    else
+        factorial::BigInt = n * factorial_recursive(n - 1)
+        return factorial
+    end
+end

test/math.jl

@@ -129,6 +129,16 @@ end
     @test euler_method((x, t) -> x, 1, (0, 5))[1][end] == 143.33937864611195
 end
 
+@testset "Math: Factorial Related" begin
+    @test factorial_iterative(5) == 120
+    @test_throws ErrorException factorial_iterative(0.1)
+    @test_throws ErrorException  factorial_iterative(-1)
+
+    @test factorial_recursive(5) == 120
+    @test_throws ErrorException  factorial_recursive(0.1)
+    @test_throws ErrorException  factorial_recursive(-1)
+end
+
 @testset "Math: Line Length" begin
     # Arc Lengths
     @test line_length(x -> x, 0, 1, 10) == 1.4142135623730947