61 lines
1.5 KiB
PHP
61 lines
1.5 KiB
PHP
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<?php
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function is_prime($prime) {
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if($prime < 1)
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return false;
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if($prime == 1)
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return true;
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if($prime == 2)
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return true;
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$sqrt = sqrt($prime);
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for ($i = 3; $i <= $sqrt; $i+=2){
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if ($prime%$i == 0) return false;
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}
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return true;
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}
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if (($handle = fopen("primes1000000.txt", "r")) !== FALSE) {
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while (($data = fgetcsv($handle, 1000, ",")) !== FALSE) {
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if ($data[1] >= 1000000)
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break;
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//If there's an even digit (or a 5) we can instantly exclude it as when rotated it will not not be a prime.
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if (
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strpos((string) $data[1], "0") !== false ||
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strpos((string) $data[1], "2") !== false ||
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strpos((string) $data[1], "4") !== false ||
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strpos((string) $data[1], "5") !== false ||
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strpos((string) $data[1], "6") !== false ||
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strpos((string) $data[1], "8") !== false
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) {
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continue;
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}
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$primes[] = (int) $data[1];
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}
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fclose($handle);
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}
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echo "File read\n";
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$count = 1+1; //2 and 5 are primes but not included
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foreach($primes as $prime)
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{
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//echo "Now testing $prime\n";
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$newprime = $prime;
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for($rotate = 1; $rotate < strlen($prime); $rotate++)
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{
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$newprime = substr($newprime, -1, 1).substr($newprime, 0, -1);
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//echo "New prime: $newprime\n";
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if(!in_array($newprime, $primes))
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{
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continue 2;
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}
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}
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$count++;
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echo $prime.PHP_EOL;
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}
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echo "Total: $count\n";
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