New exercise: prime-factors (JuliaLang#184)

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this is a trivial syntax error.

Co-Authored-By: Sascha Mann <git@mail.saschamann.eu>

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Co-Authored-By: Sascha Mann <git@mail.saschamann.eu>

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Co-Authored-By: Sascha Mann <git@mail.saschamann.eu>

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Co-Authored-By: Sascha Mann <git@mail.saschamann.eu>

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config.json

@@ -516,6 +516,17 @@
                 "loops",
                 "strings"
             ]
+        },
+        {
+            "slug": "prime-factors",
+            "uuid": "b6b7e95b-c4ca-438c-a5e7-d76cb44e5b19",
+            "core": false,
+            "unlocked_by": null,
+            "difficulty": 1,
+            "topics": [
+                "math",
+                "integers"
+            ]
         }
     ]
 }

exercises/prime-factors/README.md

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+# Prime Factors
+
+Compute the prime factors of a given natural number.
+
+A prime number is only evenly divisible by itself and 1.
+
+Note that 1 is not a prime number.
+
+## Example
+
+What are the prime factors of 60?
+
+- Our first divisor is 2. 2 goes into 60, leaving 30.
+- 2 goes into 30, leaving 15.
+  - 2 doesn't go cleanly into 15. So let's move on to our next divisor, 3.
+- 3 goes cleanly into 15, leaving 5.
+  - 3 does not go cleanly into 5. The next possible factor is 4.
+  - 4 does not go cleanly into 5. The next possible factor is 5.
+- 5 does go cleanly into 5.
+- We're left only with 1, so now, we're done.
+
+Our successful divisors in that computation represent the list of prime
+factors of 60: 2, 2, 3, and 5.
+
+You can check this yourself:
+
+- 2 * 2 * 3 * 5
+- = 4 * 15
+- = 60
+- Success!
+
+## Source
+
+The Prime Factors Kata by Uncle Bob [http://butunclebob.com/ArticleS.UncleBob.ThePrimeFactorsKata](http://butunclebob.com/ArticleS.UncleBob.ThePrimeFactorsKata)
+
+## Version compatibility
+This exercise has been tested on Julia versions >=1.0.
+
+## Submitting Incomplete Solutions
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.

exercises/prime-factors/example.jl

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+function isprime(n)
+    if n == 1
+        return false
+    elseif n == 2
+        return true
+    else
+        for i = 2:(n ^ (0.5)) + 1
+            if n % i == 0
+                return false
+            end
+        end
+        return true
+    end
+end
+
+function prime_factors(n)
+    count = 0
+    final = [1]
+    k = n
+    if n == 1
+        return []
+    end
+    while k != 1
+        count += 1
+        if k % count == 0 && isprime(count) == true
+            k = k/count
+            final = [final; [count]]
+            count = 0
+        end
+
+
+    end
+    return final[2:end]
+end

exercises/prime-factors/prime-factors.jl

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+

exercises/prime-factors/runtests.jl

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+# canonical data version 1.1.0
+include("prime-factors.jl")
+using Test
+
+@testset "no factors" begin
+    @test prime_factors(1) == []
+end
+
+@testset "prime number" begin
+    @test prime_factors(2) == [2]
+end
+
+@testset "square of a prime" begin
+    @test prime_factors(9) == [3, 3]
+end
+
+@testset "cube of a prime" begin
+    @test prime_factors(8) == [2, 2, 2]
+end
+
+@testset "product of primes and non-primes" begin
+    @test prime_factors(12) == [2, 2, 3]
+end
+
+@testset "product of primes" begin
+    @test prime_factors(901255) == [5, 17, 23, 461]
+end
+
+@testset "factors include a large prime" begin
+    @test prime_factors(93819012551) == [11, 9539, 894119]
+end