lightoj 1203(凸包)

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <vector>
#include <cmath>
using namespace std;
const double eps = 1e-9;
const double PI = acos(-1);

double Sqr(double x) { return x * x; }
int dcmp(double x) { if (fabs(x) < eps) return 0; return x > 0 ? 1 : -1; }

struct Point {
double x, y;
Point(double a = 0, double b = 0): x(a), y(b) {}
};

typedef Point Vector;
typedef vector<Point> Polygon;

Vector operator + (const Vector& a, const Vector& b) { return Vector(a.x + b.x, a.y + b.y); }
Vector operator - (const Vector& a, const Vector& b) { return Vector(a.x - b.x, a.y - b.y); }
Vector operator * (const Vector& a, double b) { return Vector(a.x * b, a.y * b); }
Vector operator / (const Vector& a, double b) { return Vector(a.x / b, a.y / b); }
bool operator == (const Vector& a, const Vector& b) { return !dcmp(a.x - b.x) && !dcmp(a.y - b.y); }
bool operator < (const Vector& a, const Vector& b) { return a.x < b.x || (a.x == b.x && a.y < b.y); }
double Dot(const Vector& a, const Vector& b) { return a.x * b.x + a.y * b.y; }
double Length(const Vector& a) { return sqrt(Dot(a, a)); }
double Cross(const Vector& a, const Vector& b) { return a.x * b.y - a.y * b.x; }
double Angle(const Vector& a, const Vector& b) { return acos(Dot(a, b) / Length(a) / Length(b)); }
double angle(Vector v) { return atan2(v.y, v.y); }

int ConvexHull(Point* P, int cnt, Point* res) {
sort(P, P + cnt);
cnt = unique(P, P + cnt) - P;
int m = 0;
for (int i = 0; i < cnt; i++) {
while (m > 1 && Cross(res[m - 1] - res[m - 2], P[i] - res[m - 2]) <= 0)
m--;
res[m++] = P[i];
}
int k = m;
for (int i = cnt - 2; i >= 0; i--) {
while (m > k && Cross(res[m - 1] - res[m - 2], P[i] - res[m - 2]) <= 0)
m--;
res[m++] = P[i];
}
if (cnt > 1) m--;
return m;
}
const int N = 1e5 + 5;
int n;
Point P
, res
;

int main() {
int t, cas = 1;
scanf("%d", &t);
while (t--) {
scanf("%d", &n);
for (int i = 0; i < n; i++)
scanf("%lf%lf", &P[i].x, &P[i].y);
int cnt = ConvexHull(P, n, res);
if (cnt < 3) {
printf("Case %d: 0\n", cas++);
continue;
}
res[cnt] = res[0];
res[cnt + 1] = res[1];
double ans = 2 * PI;
for (int i = 1; i <= cnt; i++)
ans = min(ans, Angle(res[i - 1] - res[i], res[i + 1] - res[i]));
printf("Case %d: %.10lf\n", cas++, ans * 180 / PI);
}
return 0;
}