68 lines
1.5 KiB
Markdown
68 lines
1.5 KiB
Markdown
---
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title: "Sieve of Eratosthenes"
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description: "Sieve of Eratosthenes."
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navigation: false
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date: "2021-03-02 02:31:16"
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img: "/img/algorithms/sieve-of-eratosthenes.gif"
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tags:
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- Algorithm
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---
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Implementation of the ancient sieve of Eratosthenes math algorithm, used for
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finding prime numbers up to a given limit.
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```c
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#include <stdbool.h> // bool
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#include <stdio.h> // printf
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#include <string.h> // memset
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int main(int argc, char* argv[]) {
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int limit = 10000;
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int calculate = limit * 20;
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// Create an array and set all to true
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bool numbers[calculate];
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memset(&numbers, true, sizeof(bool) * calculate);
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// Loop through all the numbers
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for (int i = 2; i < calculate; i++) {
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// Already crossed out numbers don't have to be checked
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if (numbers[i]) {
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// Cross out all the numbers that can't be a prime, which are multiples of itself
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for (int j = i * i; j < calculate; j += i) {
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numbers[j] = false;
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}
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// Once you exceed the calculate range, you can exit the loop
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if (i * i > calculate) {
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break;
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}
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}
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}
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int sum = 0;
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int counter = 1;
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// Get the sum of the first 10000 primes
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for (int i = 2; i < calculate; i++) {
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if (numbers[i]) {
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sum += i;
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if (counter >= limit) {
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break;
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}
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counter++;
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}
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}
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printf("sum of first %d primes is: %d\n", counter, sum);
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return 0;
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}
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```
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Source:<br>
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[https://en.wikipedia.org/wiki/Sieve_of_Eratosthenes](https://en.wikipedia.org/wiki/Sieve_of_Eratosthenes){ target=_blank }
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