Data commit

Task/Long-primes/Go/long-primes.go

@@ -0,0 +1,70 @@
+package main
+
+import "fmt"
+
+func sieve(limit int) []int {
+    var primes []int
+    c := make([]bool, limit + 1) // composite = true
+    // no need to process even numbers
+    p := 3
+    p2 := p * p
+    for p2 <= limit {
+        for i := p2; i <= limit; i += 2 * p {
+            c[i] = true
+        }
+        for ok := true; ok; ok = c[p] {
+            p += 2
+        }
+        p2 = p * p
+    }
+    for i := 3; i <= limit; i += 2 {
+        if !c[i] {
+            primes = append(primes, i)
+        }
+    }
+    return primes
+}
+
+// finds the period of the reciprocal of n
+func findPeriod(n int) int {
+    r := 1
+    for i := 1; i <= n + 1; i++ {
+        r = (10 * r) % n
+    }
+    rr := r
+    period := 0
+    for ok := true; ok; ok = r != rr {
+        r = (10 * r) % n
+        period++
+    }
+    return period
+}
+
+func main() {
+    primes := sieve(64000)
+    var longPrimes []int
+    for _, prime := range primes {
+        if findPeriod(prime) == prime - 1 {
+            longPrimes = append(longPrimes, prime)
+        }
+    }
+    numbers := []int{500, 1000, 2000, 4000, 8000, 16000, 32000, 64000}
+    index := 0
+    count := 0
+    totals := make([]int, len(numbers))
+    for _, longPrime := range longPrimes {
+        if longPrime > numbers[index] {
+            totals[index] = count
+            index++
+        }
+        count++
+    }
+    totals[len(numbers)-1] = count
+    fmt.Println("The long primes up to", numbers[0], "are: ")
+    fmt.Println(longPrimes[:totals[0]])
+
+    fmt.Println("\nThe number of long primes up to: ")
+    for i, total := range totals {
+        fmt.Printf("  %5d is %d\n", numbers[i], total)
+    }
+}