UVa 1473 Dome of Circus（求凸包）

#include <iostream>
#include <stdlib.h>
#include <stdio.h>
#include <math.h>
#include <algorithm>
#define INF 0x7f7f7f7f

using namespace std;

const double eps = 1e-8;
const double pi = acos(-1.0);
const int maxn = 10010;

int sig(double argu)
{
return (argu > eps) - (argu < -eps);
}

typedef struct Point
{
double x, y;
Point (double _x = 0.0, double _y = 0.0):
x(_x), y(_y) {}
Point operator +(const Point &argu) const
{
return Point(x + argu.x, y + argu.y);
}
Point operator -(const Point &argu) const
{
return Point(x - argu.x, y - argu.y);
}
Point operator *(const double k) const
{
return Point(x * k, y * k);
}
Point operator /(const double k) const
{
return Point(x / k, y / k);
}
double operator ^(const Point &argu) const
{
return (x * argu.y - y * argu.x);
}
bool operator <(const Point &argu) const
{
if(sig(y - argu.y) == 0)
return x < argu.x;
else
return y < argu.y;
}
}Vector;

int n;
Point pp[maxn], minp;
double x, y, z;
int q[maxn], top;
double h, r;
double s[maxn], best;
int id;

bool cmp(Point a, Point b)
{
double anga = atan2(a.y - minp.y, a.x - minp.x);
double angb = atan2(b.y - minp.y, b.x - minp.x);
return anga < angb;
}

double Cross(Point a, Point b, Point c)
{
return ((b - c) ^ (a - c));
}

void GetHull()
{
for(int i = 2; i < n; i++)
{
while(top > 1 && Cross(pp[i], pp[q[top - 1]], pp[q[top - 2]]) < 0)
top--;
q[top++] = i;
}
}

void GetBV(int id)
{
if(id == 0)
{
best = pi * (1.5 * pp[0].x) * (1.5 * pp[0].x) * pp[0].y;
h = 3.0 * pp[0].y;
r = 1.5 * pp[0].x;
}
else if(id == 1)
{
if(best < pi * (1.5 * pp[q[1]].x) * (1.5 * pp[q[1]].x) * pp[q[1]].y)
{
best = pi * (1.5 * pp[q[1]].x) * (1.5 * pp[q[1]].x) * pp[q[1]].y;
h = 3.0 * pp[q[1]].y;
r = 1.5 * pp[q[1]].x;
}
}
else
{
double k = atan2(2 * pp[q[id]].y, -pp[q[id]].x);
double kl = atan2(pp[q[id]].y - pp[q[id - 1]].y, pp[q[id]].x - pp[q[id - 1]].x);
double kr = atan2(pp[q[id + 1]].y - pp[q[id]].y, pp[q[id + 1]].x - pp[q[id]].x);
if(sig(kr - pi) >= 0 && sig(k - kr) >= 0)
k = kr;
if(sig(kl - pi) >= 0 && sig(kl - k) >= 0)
k = kl;
double tmph = x * tan(k) + y;
double tmpr = x * y / tan(k);
double tmpv = pi * (1.5 * tmpr) * (1.5 * tmpr) * tmph;
if(best < tmpv)
{
best = tmpv;
h = tmph;
r = tmpr;
}
}
}

int main()
{
//freopen("1473.in", "r", stdin);

while(~scanf("%d", &n))
{
for(int i = 0; i < n; i++)
{
scanf("%lf%lf%lf", &x, &y, &z);
pp[i] = Point(sqrt(x * x + y * y), z);
}
minp = pp[0];
for(int i = 1; i < n; i++)
minp = min(minp, pp[i]);
sort(pp, pp + n, cmp);
q[0] = 0;
top = 1;
GetBV(0);
if(n > 1)
{
q[1] = 1;
top++;
GetBV(1);
if(n > 2)
{
GetHull();
for(int i = 0; i < top; i++)
{
double base = (pp[q[i]].x - pp[q[(i + 1) % top]].x);
if(sig(base) != 0)
{
double slope = (pp[q[i]].y - pp[q[(i + 1) % top]].y) / base;
if(slope < 0.0)
GetBV(i);
}
}
}
}
printf("%.3lf %.3lf\n", h, r);
}
return 0;
}