Successive prime differences: Difference between revisions

=={{header|Kotlin}}==

{{trans|Java}}

<lang scala>private fun sieve(limit: Int): Array<Int> {

val primes = mutableListOf<Int>()

primes.add(2)

val c = BooleanArray(limit + 1) // composite = true

// no need to process even numbers > 2

var p = 3

while (true) {

val p2 = p * p

if (p2 > limit) {

break

}

var i = p2

while (i <= limit) {

c[i] = true

i += 2 * p

}

do {

p += 2

} while (c[p])

}

var i = 3

while (i <= limit) {

if (!c[i]) {

primes.add(i)

}

i += 2

}

return primes.toTypedArray()

}

private fun successivePrimes(primes: Array<Int>, diffs: Array<Int>): List<List<Int>> {

val results = mutableListOf<List<Int>>()

val dl = diffs.size

outer@ for (i in 0 until primes.size - dl) {

val group = IntArray(dl + 1)

group[0] = primes[i]

for (j in i until i + dl) {

if (primes[j + 1] - primes[j] != diffs[j - i]) {

continue@outer

}

group[j - i + 1] = primes[j + 1]

}

results.add(group.toList())

}

return results

}

fun main() {

val primes = sieve(999999)

val diffsList = arrayOf(

arrayOf(2),

arrayOf(1),

arrayOf(2, 2),

arrayOf(2, 4),

arrayOf(4, 2),

arrayOf(6, 4, 2)

)

println("For primes less than 1,000,000:-\n")

for (diffs in diffsList) {

println(" For differences of ${diffs.contentToString()} ->")

val sp = successivePrimes(primes, diffs)

if (sp.isEmpty()) {

println(" No groups found")

continue

}

println(" First group = ${sp[0].toTypedArray().contentToString()}")

println(" Last group = ${sp[sp.size - 1].toTypedArray().contentToString()}")

println(" Number found = ${sp.size}")

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>