2015 Challenge24 Finals: C3 (original) by HoChockiGon

#include <bits/stdc++.h>
#include <sys/time.h>

using namespace std;

#define FI first
#define SE second
#define X first
#define Y second
#define ST first
#define ND second
#define MP make_pair
#define PB push_back

typedef long long LL;
typedef vector<int> VI;
typedef long double LD;
typedef pair<int,int> PII;

#define REP(i,n) for(int i=0;i<(n);++i)
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define FORE(a,b) for(VAR(a,(b).begin());a!=(b).end();++a)
#define VAR(a,b) __typeof(b) a=(b)
#define ALL(x) (x).begin(),(x).end()
#define CLR(x,a) memset(x,a,sizeof(x))

double getTime() {
    timeval tv;
    gettimeofday(&tv, NULL);
    return tv.tv_sec + tv.tv_usec * 1e-6;
}

int d1000(int x) {
    if (x < 0) {
        return -((-x + 999) / 1000);
    } else {
        return x / 1000;
    }
}

bool should_color(int x, int y) {
    LL a = x;
    LL b = y;
    REP (i, 30) {
        LL a2 = d1000(a * a - b * b);
        LL b2 = d1000(2 * a * b);
        if (a2 > 4000) {
            return false;
        }
        a = a2 + x;
        b = b2 + y;
    }
    return true;
}

int main() {
    int x0, y0, x1, y1;
    cin >> x0 >> y0 >> x1 >> y1;
    FOR (x, x0, x1) {
        FOR (y, y0, y1) {
            if (should_color(x * 5, y * 5)) {
                cout << "X";
            } else {
                cout << ".";
            }
        }
        cout << endl;
    }
}