Submission #1280352

#	Time	Username	Problem	Language	Result	Execution time	Memory
1280352		daotuankhoi	SIR (COI15_sir)	C++20	61 / 100	116 ms	26316 KiB

sir

#include <bits/stdc++.h>

using namespace std;

#define fi first
#define se second
#define ll long long

#ifdef LOCAL
#include "algo/debug.h"
#else
#define debug(...) 42
#endif

template <class T> bool ckmax(T &a, T b) { return a < b ? (a = b, true) : false; }
template <class T> bool ckmin(T &a, T b) { return a > b ? (a = b, true) : false; }

struct Vec {
    ll x, y;
    Vec(ll _x = 0, ll _y = 0) : x(_x), y(_y) {}
    Vec operator-(Vec o) {
        return Vec(x - o.x, y - o.y);
    }
    bool operator<(Vec o) {
        return (x < o.x || (x == o.x && y < o.y));
    }
};

using Point = Vec;
ll cross(Vec a, Vec b) {
    return (a.x * b.y) - (a.y * b.x);
}

bool ccw(Point a, Point b, Point c) {
    Vec ab = b - a;
    Vec ac = c - a;
    return cross(ab, ac) > 0;
}
bool cw(Point a, Point b, Point c) {
    Vec ab = b - a;
    Vec ac = c - a;
    return cross(ab, ac) < 0;
}

bool chk(Point a, Point b, Point c) {
    Vec ab = b - a;
    Vec ac = c - a;
    return cross(ab, ac) < 0;
}

ll area(Point a, Point b, Point c) {
    array<Point, 4> e;
    e[0] = a; e[1] = b, e[2] = c, e[3] = a;
    ll ans = 0;
    for (int i = 0; i < 3; i++) {
        ans += (e[i].x * e[i+1].y) - (e[i+1].x * e[i].y);
    }
    return abs(ans);
}

const int MAXN = 3e5 + 5;
Point a[MAXN], d[MAXN];

int main() {
    #define NAME "test"
    if (fopen(NAME".inp", "r")) {
        freopen(NAME".inp", "r", stdin);
        freopen(NAME".out", "w", stdout);
    }
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    int n; cin >> n;
    for (int i = 0; i < n; i++) cin >> d[i].x >> d[i].y;
    int m; cin >> m;
    for (int i = 1; i <= m; i++) cin >> a[i].x >> a[i].y;
//    reverse(d + 1, d + n + 1);
    sort(a + 1, a + m + 1);
    vector<Point> hull;
    if (m < 3) {
        for (int i = 1; i <= m; i++) hull.emplace_back(a[i]);
    } else {
        for (int i = 1; i <= m; i++) {
            while ((int)hull.size() >= 2 && chk(hull[(int)hull.size() - 2], hull[(int)hull.size() - 1], a[i])) hull.pop_back();
            hull.emplace_back(a[i]);
        }
        int sz = hull.size();
        for (int i = m - 1; i >= 1; i--) {
            while ((int)hull.size() >= sz + 1 && chk(hull[(int)hull.size() - 2], hull[(int)hull.size() - 1], a[i])) hull.pop_back();
            hull.emplace_back(a[i]);
        }
        /// CCW
        hull.pop_back();
    }
    int cur = 0, tt = 0;
    m = hull.size();
    if (m != 1) {
        for (int i = 0; i < m; i++) {
            if (ccw(d[0], hull[i], hull[(i + 1) % m])) {
                cur = i;
                break;
            }
        }
    }
    ll s = 0;
//    cerr << calc(d[0], hull[0], hull[1]) << '\n';
//    cerr << d[0].x << ' ' << d[0].y << '\n';
//    cerr << hull[0].x << ' ' << hull[0].y << '\n';
//    cerr << hull[1].x << ' ' << hull[1].y << '\n';
//    for (auto [x, y] : hull) {
//        cout << x << ' ' << y << '\n';
//    }
    for (int i = 2; i < n; i++) {
        if (cw(d[0], hull[cur], d[i])) {
            s += area(d[0], d[i - 1], d[i]);
            tt = i;
        } else break;
    }
//    cerr << s << ' ' << tt << ' ' << cur << '\n';
//    cerr << hull[1].x << ' ' << hull[1].y << '\n';
//cerr << ccw(Point(-3, -4), Point(0, -3), Point(2, 0)) << '\n';
//cerr << ccw(d[1], hull[cur], hull[(cur + 1) % m]) << '\n';
//debug(area(Point(0, 1), Point(2, 3), Point(0, 3)));
//    assert(s != )
    ll ans = s;
    tt = max(tt + 1, 1);
    for (int i = 1; i < n; i++) {
        if (m != 1) {
            while (!ccw(d[i], hull[cur], hull[(cur + 1) % m])) {
                cur++;
                if (cur >= m) cur -= m;
            }
        }
//        cerr << i << ' ' << cur << '\n';
        s -= area(d[(i - 1 + n) % n], d[(tt - 1 + n) % n], d[i]);
//        cerr << i << '\n';
//        debug(s, area(d[i - 1], d[(tt - 1 + n) % n], d[i]));
//        debug(d[i].x, d[i].y, d[i - 1].x, d[i - 1].y, d[tt - 1].x, d[tt - 1].y);
        if (tt == i) tt = (tt + 1) % n;
//        if (tt == 1) tt = (tt + 1) % n;
        while (cw(d[i], hull[cur], d[tt])) {
            s += area(d[tt], d[(tt - 1 + n) % n], d[i]);
//            debug(tt, s, area(d[tt], d[(tt - 1 + n) % n], d[i]));
            tt++;
            tt %= n;
            if (tt == i) break;
        }
//        debug(i, tt, s);
        ckmax(ans, s);
    }
    cout << ans << '\n';
    return 0;
}

Compilation message (stderr)

sir.cpp: In function 'int main()':
sir.cpp:67:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   67 |         freopen(NAME".inp", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
sir.cpp:68:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   68 |         freopen(NAME".out", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 12 / 12
• Subtask 2: 0 / 39
• Subtask 3: 49 / 49