Add exercise: sieve (JuliaLang#23)

* Add exercise: sieve

* Fix indentation in sieve exercise

config.json

@@ -96,6 +96,17 @@
         "control-flow (if-else statements)"
       ]
     },
+    {
+      "slug": "sieve",
+      "difficulty": 2,
+      "topics": [
+        "control-flow (loops)",
+        "control-flow (conditionals)",
+        "mathematics",
+        "arrays",
+        "filtering"
+      ]
+    },
     {
       "slug": "trinary",
       "difficulty": 2,

exercises/sieve/example.jl

@@ -0,0 +1,15 @@
+function sieve(limit::Integer)
+    limit <= 0 && error("Invalid limit")
+    nums = fill(true, limit)
+    nums[1] = false
+    primes = []
+    while (i = findfirst(nums)) > 0
+        push!(primes, i)
+        for j = find(nums)
+            if j % i == 0
+                nums[j] = false
+            end
+        end
+    end
+    primes
+end

exercises/sieve/runtests.jl

@@ -0,0 +1,37 @@
+using Base.Test
+
+include("sieve.jl")
+
+@testset "no primes under two" begin
+    @test sieve(1) == []
+end
+
+@testset "find first prime" begin
+    @test sieve(2) == [2]
+end
+
+@testset "find primes up to 10" begin
+    @test sieve(10) == [2, 3, 5, 7]
+end
+
+@testset "limit is prime" begin
+    @test sieve(13) == [2, 3, 5, 7, 11, 13]
+end
+
+@testset "find primes up to 1000" begin
+    @test sieve(1000) ==  [
+        2,   3,   5,   7,   11,  13,  17,  19,  23,  29,  31,  37,  41,
+        43,  47,  53,  59,  61,  67,  71,  73,  79,  83,  89,  97,  101,
+        103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167,
+        173, 179, 181, 191, 193, 197, 199, 211, 223, 227, 229, 233, 239,
+        241, 251, 257, 263, 269, 271, 277, 281, 283, 293, 307, 311, 313,
+        317, 331, 337, 347, 349, 353, 359, 367, 373, 379, 383, 389, 397,
+        401, 409, 419, 421, 431, 433, 439, 443, 449, 457, 461, 463, 467,
+        479, 487, 491, 499, 503, 509, 521, 523, 541, 547, 557, 563, 569,
+        571, 577, 587, 593, 599, 601, 607, 613, 617, 619, 631, 641, 643,
+        647, 653, 659, 661, 673, 677, 683, 691, 701, 709, 719, 727, 733,
+        739, 743, 751, 757, 761, 769, 773, 787, 797, 809, 811, 821, 823,
+        827, 829, 839, 853, 857, 859, 863, 877, 881, 883, 887, 907, 911,
+        919, 929, 937, 941, 947, 953, 967, 971, 977, 983, 991, 997
+      ]
+end

exercises/sieve/sieve.jl

@@ -0,0 +1,3 @@
+function sieve(limit::Integer)
+
+end