Successive prime differences: Difference between revisions
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<br>Note: Generation of a list of primes is a secondary aspect of the task. Use of a built in function, well known library, or importing/use of prime generators from other [[Sieve of Eratosthenes|Rosetta Code tasks]] is encouraged.
=={{header|Go}}==
<lang go>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()
}
}</lang>
{{out}}
<pre>
For primes less than 1,000,000:-
For differences of [2] ->
First group = [3 5]
Last group = [999959 999961]
Number found = 8169
For differences of [1] ->
First group = [2 3]
Last group = [2 3]
Number found = 1
For differences of [2 2] ->
First group = [3 5 7]
Last group = [3 5 7]
Number found = 1
For differences of [2 4] ->
First group = [5 7 11]
Last group = [999431 999433 999437]
Number found = 1393
For differences of [4 2] ->
First group = [7 11 13]
Last group = [997807 997811 997813]
Number found = 1444
For differences of [6 4 2] ->
First group = [31 37 41 43]
Last group = [997141 997147 997151 997153]
Number found = 306
</pre>
=={{header|Factor}}==
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