CalmoSoft primes: Difference between revisions
Added Java solution
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Took 210 ms
</pre>
=={{header|Java}}==
{{trans|Phix}}
Uses the PrimeGenerator class from [[Extensible prime generator#Java]].
<syntaxhighlight lang="java">import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;
public class CalmoSoftPrimes {
public static void main(String[] args) {
PrimeGenerator primeGen = new PrimeGenerator(100000, 250000);
List<Integer> primes = new ArrayList<>();
final int[] limits = {100, 5000, 10000, 500000, 50000000};
long total = 0;
int last = 0;
int prime = primeGen.nextPrime();
for (int limit : limits) {
do {
primes.add(prime);
total += prime;
++last;
prime = primeGen.nextPrime();
} while (prime < limit);
long sum = total;
int longest = 1;
List<Integer> starts = new ArrayList<>();
for (int start = 0; start <= last - longest; ++start) {
long s = sum;
for (int finish = last; finish-- >= start + longest;) {
if (isPrime(s)) {
int length = finish - start + 1;
if (length > longest) {
longest = length;
starts.clear();
}
starts.add(start);
}
s -= primes.get(finish);
}
sum -= primes.get(start);
}
System.out.printf("For primes up to %d:\nThe following sequence%s of %d consecutive primes yield%s a prime sum:\n",
limit, starts.size() == 1 ? "" : "s", longest, starts.size() == 1 ? "s" : "");
for (int i = 0; i < starts.size(); ++i) {
int start = starts.get(i);
sum = 0;
for (int j = start; j < start + longest; ++j)
sum += primes.get(j);
final String separator = " + ";
if (longest > 12) {
System.out.print(join(separator, primes.subList(start, start + 6))
+ separator + "..." + separator
+ join(separator, primes.subList(start + longest - 6, start + longest)));
} else {
System.out.print(join(separator, primes.subList(start, start + longest)));
}
System.out.println(" = " + sum);
}
System.out.println();
}
}
private static <T> String join(String separator, List<T> list) {
return list.stream().map(Object::toString).collect(Collectors.joining(separator));
}
private static boolean isPrime(long n) {
if (n < 2)
return false;
if (n % 2 == 0)
return n == 2;
if (n % 3 == 0)
return n == 3;
for (long p = 5; p * p <= n; p += 4) {
if (n % p == 0)
return false;
p += 2;
if (n % p == 0)
return false;
}
return true;
}
}</syntaxhighlight>
{{out}}
<pre>
For primes up to 100:
The following sequence of 21 consecutive primes yields a prime sum:
7 + 11 + 13 + 17 + 19 + 23 + ... + 67 + 71 + 73 + 79 + 83 + 89 = 953
For primes up to 5000:
The following sequence of 665 consecutive primes yields a prime sum:
7 + 11 + 13 + 17 + 19 + 23 + ... + 4957 + 4967 + 4969 + 4973 + 4987 + 4993 = 1543127
For primes up to 10000:
The following sequences of 1223 consecutive primes yield a prime sum:
3 + 5 + 7 + 11 + 13 + 17 + ... + 9883 + 9887 + 9901 + 9907 + 9923 + 9929 = 5686633
7 + 11 + 13 + 17 + 19 + 23 + ... + 9901 + 9907 + 9923 + 9929 + 9931 + 9941 = 5706497
For primes up to 500000:
The following sequence of 41530 consecutive primes yields a prime sum:
2 + 3 + 5 + 7 + 11 + 13 + ... + 499787 + 499801 + 499819 + 499853 + 499879 + 499883 = 9910236647
For primes up to 50000000:
The following sequence of 3001117 consecutive primes yields a prime sum:
7 + 11 + 13 + 17 + 19 + 23 + ... + 49999699 + 49999711 + 49999739 + 49999751 + 49999753 + 49999757 = 72618848632313
</pre>
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