Prime Check and Prime Factors (TheAlgorithms#42)

* prime check

* prime factors

src/TheAlgorithms.jl

@@ -44,6 +44,8 @@ export line_length
 export mean
 export median
 export mode
+export prime_check
+export prime_factors
 export perfect_cube
 export perfect_number
 export perfect_square
@@ -108,6 +110,8 @@ include("math/collatz_sequence.jl")
 include("math/euler_method.jl")
 include("math/factorial.jl")
 include("math/line_length.jl")
+include("math/prime_check.jl")
+include("math/prime_factors.jl")
 include("math/perfect_cube.jl")
 include("math/perfect_number.jl")
 include("math/perfect_square.jl")

src/math/prime_check.jl

@@ -0,0 +1,40 @@
+"""
+prime_check(number)
+
+Checks to see if a number is a prime or not
+    
+A number is prime if it has exactly two factors: 1 and itself.
+
+# Example
+
+```julia
+prime_check(2) # returns true
+prime_check(3) # returns true
+prime_check(5) # returns true
+prime_check(7) # returns true
+prime_check(11) # returns true
+prime_check(13) # returns true
+prime_check(17) # returns true
+prime_check(19) # returns true
+prime_check(23) # returns true
+prime_check(29) # returns true
+```
+
+Contributed By:- [Ashwani Rathee](https://github.com/ashwani-rathee)
+"""
+function prime_check(number)
+    if 1 < number < 4
+        # 2, 3 are primes
+        return true
+    elseif number < 2 || number % 2 == 0
+        # Negative ,0,1, and even numbers except 2 are not primes
+        return false
+    end
+    odd_numbers = collect(3:2:trunc(sqrt(number) + 1))
+    for i in odd_numbers
+        if number % i == 0
+            return false
+        end
+    end
+    return true
+end

src/math/prime_factors.jl

@@ -0,0 +1,36 @@
+"""
+prime_factors(number)
+
+Returns prime factors of `number` as a vector
+
+# Example
+
+```julia
+prime_factors(50)          # returns [2,5,5]
+prime_factors(0)           # returns []
+prime_factors(100)         # returns [2, 2, 5, 5]
+prime_factors(2560)        # returns [2, 2, 2, 2, 2, 2, 2, 2, 2, 5]
+prime_factors(10^-2)       # returns []
+prime_factors(0.02)        # returns []
+prime_factors(10^-354)     # returns []
+prime_factors("hello")     # returns error
+```
+
+Contributed By:- [Ashwani Rathee](https://github.com/ashwani-rathee)
+"""
+function prime_factors(number)
+    i = 2
+    factors = []
+    while i^2 <= number
+        if number % i == 1
+            i += 1
+        else
+            number ÷= i
+            push!(factors, i)
+        end
+    end
+    if number > 1 == 1
+        push!(factors, number)
+    end
+    return factors
+end

test/math.jl

@@ -146,6 +146,35 @@ end
 	@test line_length(x -> sin(5 * x) + cos(10 * x) + 0.1 * x^2, 0, 10, 10000) == 69.53493003183544
 end
 
+@testset "Math: Prime Check" begin
+    @test prime_check(2) == true
+    @test prime_check(3) == true
+    @test prime_check(5) == true
+    @test prime_check(7) == true
+    @test prime_check(11) == true
+    @test prime_check(13) == true
+    @test prime_check(17) == true
+    @test prime_check(19) == true
+    @test prime_check(23) == true
+    @test prime_check(29) == true
+    @test prime_check(112) == false
+    @test prime_check(172) == false
+    @test prime_check(1231) == true
+    @test prime_check(2332) == false
+    @test prime_check(2932) == false
+end
+
+@testset "Math: Prime Factors" begin
+    @test prime_factors(50) == [2,5,5]
+    @test prime_factors(0) == []
+    @test prime_factors(100) == [2, 2, 5, 5]
+    @test prime_factors(2560) == [2, 2, 2, 2, 2, 2, 2, 2, 2, 5]
+    @test prime_factors(10^-2) == []
+    @test prime_factors(0.02) == []
+    @test prime_factors(10^-354) == []
+    @test_throws MethodError prime_factors("hello")
+ end
+
 @testset "Math: Perfect Cube" begin
     @test perfect_cube(27) == true
     @test perfect_cube(4) == false