c3c/resources/examples/fannkuch-redux.c3

module fannkuch;
import std::array;
import libc;
import std::mem;

macro int max(int a, int b)
{
    return a > b ? a : b;
}

fn int fannkuchredux(int n)
{
    int* perm = @array::make(int, n);
    int* perm1 = @array::make(int, n);
    int* count = @array::make(int, n);
    int max_flips_count;
    int perm_count;
    int checksum;

    for (int i = 0; i < n; i++) perm1[i] = i;

    int r = n;

    while (1)
    {
        for (; r != 1; r--) count[r - 1] = r;

        for (int i = 0; i < n; i++) perm[i] = perm1[i];

        int flips_count = 0;
        int k;

        while (!((k = perm[0]) == 0))
        {
            int k2 = (k + 1) >> 1;
            for (int i = 0; i < k2; i++)
            {
                int temp = perm[i];
                perm[i] = perm[k - i];
                perm[k - i] = temp;
            }
            flips_count++;
        }

        max_flips_count = @max(max_flips_count, flips_count);
        checksum += perm_count % 2 == 0 ? flips_count : -flips_count;

        /* Use incremental change to generate another permutation */
        while (1)
        {
            if (r == n)
            {
                libc::printf("%d\n", checksum);
                return max_flips_count;
            }

            int perm0 = perm1[0];
            int i = 0;
            while (i < r)
            {
                int j = i + 1;
                perm1[i] = perm1[j];
                i = j;
            }
            perm1[r] = perm0;
            count[r] = count[r] - 1;
            if (count[r] > 0) break;
            r++;
        }
        perm_count++;
    }
    return 0;
}

fn int main(int argc, char** argv)
{
    int n = argc > 1 ? libc::atoi(argv[1]) : 7;
    libc::printf("Pfannkuchen(%d) = %d\n", n, fannkuchredux(n));
    return 0;
}