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fix: rewrite prime numbers using linear sieve (#1810)

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* fix: rewrite prime numbers using linear sieve

* fix code scanning error

* clang-format and clang-tidy fixes for 0afd463b

* fix sign-compare warning

* clang-format and clang-tidy fixes for 6ddff0f7

Co-authored-by: David Leal <halfpacho@gmail.com>
Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
This commit is contained in:
Allen Guan 2021-11-01 07:47:16 +08:00 committed by GitHub
parent 4e3abd4601
commit 1f6c39bcf2
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1 changed files with 17 additions and 9 deletions
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26
math/prime_numbers.cpp
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@ -9,14 +9,22 @@
/** Generate an increasingly large number of primes
* and store in a list
*/
std::vector<int> primes(int max) {
max++;
std::vector<int> primes(size_t max) {
std::vector<int> res;
std::vector<bool> numbers(max, false);
for (int i = 2; i < max; i++) {
if (!numbers[i]) {
for (int j = i; j < max; j += i) numbers[j] = true;
res.push_back(i);
std::vector<bool> is_not_prime(max + 1, false);
for (size_t i = 2; i <= max; i++) {
if (!is_not_prime[i]) {
res.emplace_back(i);
}
for (int p : res) {
size_t k = i * p;
if (k > max) {
break;
}
is_not_prime[k] = true;
if (i % p == 0) {
break;
}
}
}
return res;
@ -25,9 +33,9 @@ std::vector<int> primes(int max) {
/** main function */
int main() {
std::cout << "Calculate primes up to:\n>> ";
int n;
int n = 0;
std::cin >> n;
std::vector<int> ans = primes(n);
for (int i = 0; i < ans.size(); i++) std::cout << ans[i] << ' ';
for (int p : ans) std::cout << p << ' ';
std::cout << std::endl;
}