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[Sieve of Eratosthenes in C] #algorithm
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/** | |
* sieve.c | |
* | |
* Created by Jay Lee on 08/25/2019. | |
* Copyright © 2019 Jay Lee <jaeho.lee@snu.ac.kr> | |
* This work is free. You can redistribute it and/or modify it under the | |
* terms of the Do What The Fuck You Want To Public License, Version 2, | |
* as published by Sam Hocevar. See http://www.wtfpl.net/ for more details. | |
*/ | |
#include <stdio.h> | |
#include <stdlib.h> | |
#include <stdbool.h> | |
#include <math.h> | |
#include <time.h> | |
#define SIZE 10000 | |
void generate_sieve(bool *sieve, int cnt) | |
{ | |
int bound = sqrt(cnt - 1); | |
for (int p = 2; p <= bound; ++p) { | |
if (!sieve[p]) { | |
for (int n = p * p; n < cnt; n += p) { | |
sieve[n] = true; | |
} | |
} | |
} | |
} | |
int main(void) | |
{ | |
clock_t start = clock(); | |
/* malloc for large SIZE's */ | |
bool *sieve = malloc(sizeof(bool[SIZE])); | |
sieve[0] = sieve[1] = true; | |
generate_sieve(sieve, SIZE); | |
int cnt = 0; | |
int i, j; | |
for (i = 0; i < SIZE; ++i) { | |
cnt += !sieve[i]; | |
} | |
int *primes = malloc(sizeof(int[SIZE])); | |
for (i = j = 0; i < SIZE; ++i) { | |
if (!sieve[i]) { | |
primes[j++] = i; | |
printf("%d ", i); | |
} | |
} | |
printf("\n"); | |
free(sieve); | |
free(primes); | |
clock_t end = clock(); | |
float seconds = (float)(end - start) / CLOCKS_PER_SEC; | |
printf("Took %f seconds\n", seconds); | |
return 0; | |
} |
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