HDU 1348 (凸包)

题意是求凸包的周长加上一个半径为l的圆周长。

板子题。

#include <bits/stdc++.h>
using namespace std;
typedef unsigned long long ll;
#define maxn 1111
#define pi acos (-1)

struct point {
    double x, y;
    point (double _x = 0, double _y = 0) : x(_x), y(_y) {}
    point operator - (point a) const {
        return point (x-a.x, y-a.y);
    }
    bool operator < (const point &a) const {
        return x < a.x || (x == a.x && y < a.y);
    }
}p[maxn];

const double eps = 1e-10;
int dcmp (double x) {
    if (fabs (x) < eps)
        return 0;
    else return x < 0 ? -1 : 1;
}
double cross (point a, point b) {
    return a.x*b.y-a.y*b.x;
}
double dot (point a, point b) {
    return a.x*b.x + a.y*b.y;
}

int n, m;
double l;
point ch[maxn];

int ConvexHull () {
    sort (p, p+n);
    int m = 0;
    for (int i = 0; i < n; i++) {
        while (m > 1 && cross (ch[m-1]-ch[m-2], p[i]-ch[m-1]) <= 0)
            m--;
        ch[m++] = p[i];
    }
    int k = m;
    for (int i = n-2; i >= 0; i--) {
        while (m > k && cross (ch[m-1]-ch[m-2], p[i]-ch[m-1]) <= 0)
            m--;
        ch[m++] = p[i];
    }
    if (n > 1)
        m--;
    return m;
}

double dis (point a, point b) {
    double xx = a.x-b.x, yy = a.y-b.y;
    return sqrt (xx*xx + yy*yy);
}

int main () {
    //freopen ("in", "r", stdin);
    int t, kase = 0;
    scanf ("%d", &t);
    while (t--) {
        if (kase++)
            printf ("\n");
        scanf ("%d%lf", &n, &l);
        for (int i = 0; i < n; i++) {
            scanf ("%lf%lf", &p[i].x, &p[i].y);
        }
        m = ConvexHull ();
        double ans = 0;
        for (int i = 0; i < m; i++) {
            ans += dis (ch[i], ch[(i+1)%m]);
        }
        ans += 2*pi*l;
        printf ("%lld\n", (long long) (ans+0.5));
    }
    return 0;
}