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authorDimitri Sokolyuk <demon@dim13.org>2016-08-27 23:44:29 +0200
committerDimitri Sokolyuk <demon@dim13.org>2016-08-27 23:44:29 +0200
commita593ae4ca4e3af5c419461284c97a6cc91466d1b (patch)
treefda052eedb8036260a226cb61f15733e67b1a30f
parent4f1bb81b4401686fa8860756a68c81a7b292008a (diff)
Solve sieve
-rw-r--r--go/largest-series-product/x19
-rw-r--r--go/sieve/README.md45
-rw-r--r--go/sieve/sieve.go20
-rw-r--r--go/sieve/sieve_test.go36
4 files changed, 101 insertions, 19 deletions
diff --git a/go/largest-series-product/x b/go/largest-series-product/x
deleted file mode 100644
index ef92038..0000000
--- a/go/largest-series-product/x
+++ /dev/null
@@ -1,19 +0,0 @@
-1234567890
-
-123
- 234
- 345
- 456
- 567
- 678
- 789
- 890
-
-10 - 3 + 1
-
-12345
- 23456
- 34567
- 45678
- 56789
- 67890
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)
+ }
+}