52 lines
1.6 KiB
Text
52 lines
1.6 KiB
Text
// version 1.1.51
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import java.util.stream.Collectors
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/* returns the number itself, its smallest prime factor and all its prime factors */
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fun primeFactorInfo(n: Int): Triple<Int, Int, List<Int>> {
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if (n <= 1) throw IllegalArgumentException("Number must be more than one")
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if (isPrime(n)) return Triple(n, n, listOf(n))
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val factors = mutableListOf<Int>()
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var factor = 2
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var nn = n
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while (true) {
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if (nn % factor == 0) {
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factors.add(factor)
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nn /= factor
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if (nn == 1) return Triple(n, factors.min()!!, factors)
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if (isPrime(nn)) factor = nn
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}
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else if (factor >= 3) factor += 2
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else factor = 3
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}
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}
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fun isPrime(n: Int) : Boolean {
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if (n < 2) return false
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if (n % 2 == 0) return n == 2
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if (n % 3 == 0) return n == 3
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var d = 5
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while (d * d <= n) {
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if (n % d == 0) return false
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d += 2
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if (n % d == 0) return false
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d += 4
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}
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return true
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}
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fun main(args: Array<String>) {
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val numbers = listOf(
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12757923, 12878611, 12878893, 12757923, 15808973, 15780709, 197622519
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)
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val info = numbers.stream()
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.parallel()
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.map { primeFactorInfo(it) }
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.collect(Collectors.toList())
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val maxFactor = info.maxBy { it.second }!!.second
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val results = info.filter { it.second == maxFactor }
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println("The following number(s) have the largest minimal prime factor of $maxFactor:")
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for (result in results) {
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println(" ${result.first} whose prime factors are ${result.third}")
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}
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}
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