71 lines
1.7 KiB
C++
71 lines
1.7 KiB
C++
#include <cmath>
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#include <vector>
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#include <algorithm>
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#include <iostream>
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void sieve(std::vector<int>& primes, int const limit) {
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if (limit < 2) {
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return;
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} else if (limit < 3) {
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primes.push_back(2);
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return;
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}
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primes.push_back(2);
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primes.push_back(3);
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for (int num = 5; num <= limit; num += 2) {
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int sqrtnum = (int) std::sqrt(num);
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bool isPrime = true;
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for (auto primeIt = ++primes.begin(); primeIt != primes.end() && *primeIt <= sqrtnum; ++primeIt) {
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if (num % *primeIt == 0) {
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isPrime = false;
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break;
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}
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}
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if (isPrime) {
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primes.push_back(num);
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}
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}
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}
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int main(void) {
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constexpr int limit = 1000000;
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constexpr int PRIMELIMIT = limit - 1;
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std::vector<int> primes;
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sieve(primes, PRIMELIMIT);
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std::vector<int> circular;
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auto primeIt = primes.begin();
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while (*primeIt < 10) {
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circular.push_back(*primeIt);
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++primeIt;
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}
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int tens = 10;
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int nextTens = 100;
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int rotations = 2;
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while (primeIt != primes.end()) {
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if (*primeIt >= nextTens) {
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tens *= 10;
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nextTens *= 10;
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++rotations;
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}
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bool isCircular = true;
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int prime = *primeIt;
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for (int i = 1; i < rotations; ++i) {
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prime = prime / 10 + (prime % 10) * tens;
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isCircular = std::binary_search(primes.begin(), primes.end(), prime)? true: false;
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if (!isCircular) {
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break;
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}
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}
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if (isCircular) {
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circular.push_back(*primeIt);
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}
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++primeIt;
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}
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std::cout << circular.size() << std::endl;
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}
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