LightOJ 1239 Convex Fence (Convex Hull)

Jan's LightOJ :: Problem 1239 - Convex Fence

　　简单凸包，练手题。

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <cmath>
#include <iostream>

using namespace std;

typedef long long LL;

struct Point {
    LL x, y;
    Point() {}
    Point(LL x, LL y) : x(x), y(y) {}
} ;

bool operator < (Point x, Point y) { return x.x < y.x || (x.x == y.x && x.y < y.y);}
Point operator - (Point x, Point y) { return Point(x.x - y.x, x.y - y.y);}

inline LL crossDet(Point a, Point b) { return a.x * b.y - a.y * b.x;}
inline LL crossDet(Point o, Point a, Point b) { return crossDet(a - o, b - o);}

int andrew(Point *pt, int n, Point *ch) {
    sort(pt, pt + n);
    int m = 0;
    for (int i = 0; i < n; i++) {
        while (m > 1 && crossDet(ch[m - 2], ch[m - 1], pt[i]) <= 0) m--;
        ch[m++] = pt[i];
    }
    int k = m;
    for (int i = n - 2; i >= 0; i--) {
        while (m > k && crossDet(ch[m - 2], ch[m - 1], pt[i]) <= 0) m--;
        ch[m++] = pt[i];
    }
    if (m > 1) m--;
    return m;
}

template <class T> T sqr(T x) { return x * x;}

double ptDis(Point x, Point y) {
    double dx = x.x - y.x;
    double dy = x.y - y.y;
    return sqrt(sqr(dx) + sqr(dy));
}

const double PI = acos(-1.0);
const int N = 55555;
Point pt[N], ch[N];

int main() {
//    freopen("in", "r", stdin);
    int n, d, T;
    cin >> T;
    for (int cas = 1; cas <= T; cas++) {
        cin >> n >> d;
        for (int i = 0; i < n; i++) {
            scanf("%lld%lld", &pt[i].x, &pt[i].y);
        }
        n = andrew(pt, n, ch);
        ch[n] = ch[0];
        double sum = 0.0;
        for (int i = 0; i < n; i++) {
            sum += ptDis(ch[i], ch[i + 1]);
        }
        printf("Case %d: %.9f\n", cas, sum + 2.0 * PI * d);
    }
    return 0;
}

——written by Lyon