graphs/piscine/sieve_eratosthenes_advanced/sieve.c


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#include <stdio.h>
#include <stdlib.h>

void sieve(int n)
{
    if (n <= 2)
    {
        return;
    }

    // Generate array
    int *a = calloc(n, sizeof(int));
    int count = 0;

    // Actual sieve and count
    for (int i = 2; i < n; i++)
    {
        if (a[i] == 0)
        {
            for (int k = 2 * i; k < n; k += i)
            {
                a[k] = 1;
            }
        }
    }

    for (int i = 2; i < n; i++)
    {
        if (a[i] == 0)
        {
            count++;
        }
    }

    // Print the count
    printf("%d\n", count);

    free(a);
}