OpenCup :: Stage 8 - GP of America :: Problem C

#include <cstdio>
#include <algorithm>
#include <memory.h>

using namespace std;

typedef long long ll;

ll gcd(ll a, ll b) {
    if (a < b) swap(a, b);
    while (b) {
        a %= b;
        swap(a, b);
    }
    return a;
}

ll lcm(ll a, ll b) {
    return a / gcd(a, b) * b;
}

int n, k, x, y, a[888][888], p[888], cc, tt;
ll ans, cur;
bool w[888];

int main() {
    freopen("doubledealing.in", "r", stdin);
    freopen("doubledealing.out", "w", stdout);
    tt = 0;
    while (1) {
        scanf("%d%d", &n, &k);
        if (!n) break;
        if (n <= k) {
            printf("1\n");
            continue;
        }
        x = 1;
        y = 1;
        for (int i = 1; i <= n; ++i) {
            a[x][y++] = i;
            if (y > k) {
                ++x;
                y = 1;
            }
        }
        y = k;
        x = 1;
        cc = n;
        while (y)
            if (!a[x][y] || a[x][y] > n) {
                --y;
                x = 1;
            } else p[a[x++][y]] = cc--;
        ans = 1;
        memset(w, 1, sizeof(w));
        for (int i = 1; i <= n; ++i)
            if (w[i]) {
                cur = 1;
                x = p[i];
                w[i] = false;
                while (w[x]) {
                    w[x] = false;
                    ++cur;
                    x = p[x];
                }
                ans = lcm(ans, cur);
            }
        printf("%lld\n", ans);
        x = 1;
        for (int i = 1; i <= n; ++i) {
            a[x][y++] = 0;
            if (y > k) {
                ++x;
                y = 1;
            }
        }
    }
    return 0;
}