From a593ae4ca4e3af5c419461284c97a6cc91466d1b Mon Sep 17 00:00:00 2001 From: Dimitri Sokolyuk Date: Sat, 27 Aug 2016 23:44:29 +0200 Subject: Solve sieve --- go/sieve/README.md | 45 +++++++++++++++++++++++++++++++++++++++++++++ go/sieve/sieve.go | 20 ++++++++++++++++++++ go/sieve/sieve_test.go | 36 ++++++++++++++++++++++++++++++++++++ 3 files changed, 101 insertions(+) create mode 100644 go/sieve/README.md create mode 100644 go/sieve/sieve.go create mode 100644 go/sieve/sieve_test.go (limited to 'go/sieve') diff --git a/go/sieve/README.md b/go/sieve/README.md new file mode 100644 index 0000000..b76623b --- /dev/null +++ b/go/sieve/README.md @@ -0,0 +1,45 @@ +# Sieve + +Write a program that uses the Sieve of Eratosthenes to find all the primes from 2 up to a given number. + +The Sieve of Eratosthenes is a simple, ancient algorithm for finding all +prime numbers up to any given limit. It does so by iteratively marking as +composite (i.e. not prime) the multiples of each prime, +starting with the multiples of 2. + +Create your range, starting at two and continuing up to and including the given limit. (i.e. [2, limit]) + +The algorithm consists of repeating the following over and over: + +- take the next available unmarked number in your list (it is prime) +- mark all the multiples of that number (they are not prime) + +Repeat until you have processed each number in your range. + +When the algorithm terminates, all the numbers in the list that have not +been marked are prime. + +The wikipedia article has a useful graphic that explains the algorithm: +https://en.wikipedia.org/wiki/Sieve_of_Eratosthenes + +Notice that this is a very specific algorithm, and the tests don't check +that you've implemented the algorithm, only that you've come up with the +correct list of primes. + +To run the tests simply run the command `go test` in the exercise directory. + +If the test suite contains benchmarks, you can run these with the `-bench` +flag: + + go test -bench . + +For more detailed info about the Go track see the [help +page](http://exercism.io/languages/go). + +## Source + +Sieve of Eratosthenes at Wikipedia [http://en.wikipedia.org/wiki/Sieve_of_Eratosthenes](http://en.wikipedia.org/wiki/Sieve_of_Eratosthenes) + +## Submitting Incomplete Problems +It's possible to submit an incomplete solution so you can see how others have completed the exercise. + diff --git a/go/sieve/sieve.go b/go/sieve/sieve.go new file mode 100644 index 0000000..3f69c03 --- /dev/null +++ b/go/sieve/sieve.go @@ -0,0 +1,20 @@ +package sieve + +func Sieve(n int) []int { + p := make([]int, n-1) + // initialize + for i := range p { + p[i] = i + 2 + } + // sieve + var ret []int + for _, v := range p { + if v != 0 { + for i := 2*v - 2; i < len(p); i += v { + p[i] = 0 + } + ret = append(ret, v) + } + } + return ret +} diff --git a/go/sieve/sieve_test.go b/go/sieve/sieve_test.go new file mode 100644 index 0000000..1eec072 --- /dev/null +++ b/go/sieve/sieve_test.go @@ -0,0 +1,36 @@ +package sieve + +import ( + "reflect" + "testing" +) + +var p10 = []int{2, 3, 5, 7} +var p1000 = []int{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} + +func TestSieve(t *testing.T) { + p := Sieve(10) + if !reflect.DeepEqual(p, p10) { + t.Fatalf("Sieve(10) = %v, want %v", p, p10) + } + p = Sieve(1000) + if !reflect.DeepEqual(p, p1000) { + t.Fatalf("Sieve(1000) = %v, want %v", p, p1000) + } +} + +func BenchmarkSieve(b *testing.B) { + for i := 0; i < b.N; i++ { + Sieve(1000) + } +} -- cgit v1.2.3