Data commit

Task/Successive-prime-differences/Kotlin/successive-prime-differences.kotlin

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+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()
+    }
+}