Data commit

Task/Successive-prime-differences/Go/successive-prime-differences.go

@@ -0,0 +1,69 @@
+package main
+
+import "fmt"
+
+func sieve(limit int) []int {
+    primes := []int{2}
+    c := make([]bool, limit+1) // composite = true
+    // no need to process even numbers > 2
+    p := 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
+            }
+        }
+    }
+    for i := 3; i <= limit; i += 2 {
+        if !c[i] {
+            primes = append(primes, i)
+        }
+    }
+    return primes
+}
+
+func successivePrimes(primes, diffs []int) [][]int {
+    var results [][]int
+    dl := len(diffs)
+outer:
+    for i := 0; i < len(primes)-dl; i++ {
+        group := make([]int, dl+1)
+        group[0] = primes[i]
+        for j := i; j < i+dl; j++ {
+            if primes[j+1]-primes[j] != diffs[j-i] {
+                group = nil
+                continue outer
+            }
+            group[j-i+1] = primes[j+1]
+        }
+        results = append(results, group)
+        group = nil
+    }
+    return results
+}
+
+func main() {
+    primes := sieve(999999)
+    diffsList := [][]int{{2}, {1}, {2, 2}, {2, 4}, {4, 2}, {6, 4, 2}}
+    fmt.Println("For primes less than 1,000,000:-\n")
+    for _, diffs := range diffsList {
+        fmt.Println("  For differences of", diffs, "->")
+        sp := successivePrimes(primes, diffs)
+        if len(sp) == 0 {
+            fmt.Println("    No groups found")
+            continue
+        }
+        fmt.Println("    First group   = ", sp[0])
+        fmt.Println("    Last group    = ", sp[len(sp)-1])
+        fmt.Println("    Number found  = ", len(sp))
+        fmt.Println()
+    }
+}