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ID题目提交者结果用时内存语言文件大小提交时间测评时间
#733118#9520. Concave HullcfaaaWA 0ms3760kbC++142.0kb2024-11-10 17:17:082024-11-10 17:17:08

Judging History

你现在查看的是最新测评结果

  • [2024-11-10 17:17:08]
  • 评测
  • 测评结果:WA
  • 用时:0ms
  • 内存:3760kb
  • [2024-11-10 17:17:08]
  • 提交

answer

#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>

using namespace std;

struct Point {
    long long x, y;
    bool operator<(const Point& other) const {
        return (x == other.x) ? y < other.y : x < other.x;
    }
};

// 叉积计算
long long cross(const Point& o, const Point& a, const Point& b) {
    return (a.x - o.x) * (b.y - o.y) - (a.y - o.y) * (b.x - o.x);
}

// 计算多边形面积的两倍
long long area2(const vector<Point>& poly) {
    long long res = 0;
    int n = poly.size();
    for (int i = 0; i < n; ++i) {
        int j = (i + 1) % n;
        res += poly[i].x * poly[j].y - poly[i].y * poly[j].x;
    }
    return abs(res);
}

// 凸包算法(Andrew算法)
vector<Point> convexHull(vector<Point>& points) {
    sort(points.begin(), points.end());
    vector<Point> hull;

    // 下半部分
    for (const Point& p : points) {
        while (hull.size() >= 2 && cross(hull[hull.size() - 2], hull[hull.size() - 1], p) <= 0)
            hull.pop_back();
        hull.push_back(p);
    }

    // 上半部分
    int lower = hull.size() + 1;
    for (int i = points.size() - 2; i >= 0; --i) {
        while (hull.size() >= lower && cross(hull[hull.size() - 2], hull[hull.size() - 1], points[i]) <= 0)
            hull.pop_back();
        hull.push_back(points[i]);
    }

    hull.pop_back(); // Remove the duplicate last point
    return hull;
}

int main() {
    int T;
    cin >> T;
    while (T--) {
        int n;
        cin >> n;
        vector<Point> points(n);
        for (int i = 0; i < n; ++i) {
            cin >> points[i].x >> points[i].y;
        }

        vector<Point> hull = convexHull(points);

        // 如果凸包的点数小于3,无法构成有效的凹多边形
        if (hull.size() < 3) {
            cout << 1 << endl;
            continue;
        }

        // 计算凸包面积的两倍
        long long area = area2(hull);
        
        cout << area << endl;
    }

    return 0;
}

詳細信息

Test #1:

score: 0
Wrong Answer
time: 0ms
memory: 3760kb

input:

2
6
-2 0
1 -2
5 2
0 4
1 2
3 1
4
0 0
1 0
0 1
1 1

output:

44
2

result:

wrong answer 1st lines differ - expected: '40', found: '44'