Data commit

Task/Sexy-primes/Go/sexy-primes.go

@@ -0,0 +1,113 @@
+package main
+
+import "fmt"
+
+func sieve(limit int) []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 := 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 printHelper(cat string, le, lim, max int) (int, int, string) {
+    cle, clim := commatize(le), commatize(lim)
+    if cat != "unsexy primes" {
+        cat = "sexy prime " + cat
+    }
+    fmt.Printf("Number of %s less than %s = %s\n", cat, clim, cle)
+    last := max
+    if le < last {
+        last = le
+    }
+    verb := "are"
+    if last == 1 {
+        verb = "is"
+    }
+    return le, last, verb
+}
+
+func main() {
+    lim := 1000035
+    sv := sieve(lim - 1)
+    var pairs [][2]int
+    var trips [][3]int
+    var quads [][4]int
+    var quins [][5]int
+    var unsexy = []int{2, 3}
+    for i := 3; i < lim; i += 2 {
+        if i > 5 && i < lim-6 && !sv[i] && sv[i-6] && sv[i+6] {
+            unsexy = append(unsexy, i)
+            continue
+        }
+        if i < lim-6 && !sv[i] && !sv[i+6] {
+            pair := [2]int{i, i + 6}
+            pairs = append(pairs, pair)
+        } else {
+            continue
+        }
+        if i < lim-12 && !sv[i+12] {
+            trip := [3]int{i, i + 6, i + 12}
+            trips = append(trips, trip)
+        } else {
+            continue
+        }
+        if i < lim-18 && !sv[i+18] {
+            quad := [4]int{i, i + 6, i + 12, i + 18}
+            quads = append(quads, quad)
+        } else {
+            continue
+        }
+        if i < lim-24 && !sv[i+24] {
+            quin := [5]int{i, i + 6, i + 12, i + 18, i + 24}
+            quins = append(quins, quin)
+        }
+    }
+    le, n, verb := printHelper("pairs", len(pairs), lim, 5)
+    fmt.Printf("The last %d %s:\n  %v\n\n", n, verb, pairs[le-n:])
+
+    le, n, verb = printHelper("triplets", len(trips), lim, 5)
+    fmt.Printf("The last %d %s:\n  %v\n\n", n, verb, trips[le-n:])
+
+    le, n, verb = printHelper("quadruplets", len(quads), lim, 5)
+    fmt.Printf("The last %d %s:\n  %v\n\n", n, verb, quads[le-n:])
+
+    le, n, verb = printHelper("quintuplets", len(quins), lim, 5)
+    fmt.Printf("The last %d %s:\n  %v\n\n", n, verb, quins[le-n:])
+
+    le, n, verb = printHelper("unsexy primes", len(unsexy), lim, 10)
+    fmt.Printf("The last %d %s:\n  %v\n\n", n, verb, unsexy[le-n:])
+}