Data commit

Task/Twin-primes/Go/twin-primes-1.go

@@ -0,0 +1,61 @@
+package main
+
+import "fmt"
+
+func sieve(limit uint64) []bool {
+    limit++
+    // True denotes composite, false denotes prime.
+    c := make([]bool, limit) // all false by default
+    c[0] = true
+    c[1] = true
+    // no need to bother with even numbers over 2 for this task
+    p := uint64(3) // Start from 3.
+    for {
+        p2 := p * p
+        if p2 >= limit {
+            break
+        }
+        for i := p2; i < limit; i += 2 * p {
+            c[i] = true
+        }
+        for {
+            p += 2
+            if !c[p] {
+                break
+            }
+        }
+    }
+    return c
+}
+
+func commatize(n int) string {
+    s := fmt.Sprintf("%d", n)
+    if n < 0 {
+        s = s[1:]
+    }
+    le := len(s)
+    for i := le - 3; i >= 1; i -= 3 {
+        s = s[0:i] + "," + s[i:]
+    }
+    if n >= 0 {
+        return s
+    }
+    return "-" + s
+}
+
+func main() {
+    c := sieve(1e10 - 1)
+    limit := 10
+    start := 3
+    twins := 0
+    for i := 1; i < 11; i++ {
+        for i := start; i < limit; i += 2 {
+            if !c[i] && !c[i-2] {
+                twins++
+            }
+        }
+        fmt.Printf("Under %14s there are %10s pairs of twin primes.\n", commatize(limit), commatize(twins))
+        start = limit + 1
+        limit *= 10
+    }
+}

Task/Twin-primes/Go/twin-primes-2.go

@@ -0,0 +1,29 @@
+package main
+
+import (
+    "fmt"
+    "github.com/jbarham/primegen.go"
+)
+
+func main() {
+    p := primegen.New()
+    count := 0
+    previous := uint64(0)
+    power := 1
+    limit := uint64(10)
+    for {
+        prime := p.Next()
+        if prime >= limit {
+            fmt.Printf("Number of twin prime pairs less than %d: %d\n", limit, count)
+            power++
+            if power > 10 {
+                break
+            }
+            limit *= 10
+        }
+        if previous > 0 && prime == previous + 2 {
+            count++
+        }
+        previous = prime
+    }
+}