三维凸包（已经忘光了

#include <bits/stdc++.h>
using namespace std;
typedef double db;
const int N = 2100;
const db eps = 1e-9;
int n;
int vis[N][N];
db Ran() { return rand() / (double)RAND_MAX; }
db reps() { return (Ran() - 0.5) * eps; }
struct vec
{
	db x, y, z;
	void in()
	{
		scanf("%lf%lf%lf", &x, &y, &z);
		return;
	}
	vec(db a = 0, db b = 0, db c = 0) : x(a), y(b), z(c) {}
	vec operator+(const vec r)
	{
		return vec(x + r.x, y + r.y, z + r.z);
	}
	vec operator-(const vec r)
	{
		return vec(x - r.x, y - r.y, z - r.z);
	}
	vec operator*(const vec r)
	{
		return vec(y * r.z - z * r.y, z * r.x - x * r.z, x * r.y - y * r.x);
	}
	db operator&(const vec r)
	{
		return x * r.x + y * r.y + z * r.z;
	}
} A[N];
typedef vec pon;
db dis(vec t)
{
	return sqrt(t.x * t.x + t.y * t.y + t.z * t.z);
}
void shake(pon &t)
{
	t.x += reps(), t.y += reps(), t.z += reps();
	return;
}
struct Face
{
	int v[3];
	Face() { v[0] = v[1] = v[2] = 0; }
	Face(int a, int b, int c) { v[0] = a, v[1] = b, v[2] = c; }
	vec norm()
	{
		return (A[v[1]] - A[v[0]]) * (A[v[2]] - A[v[0]]);
	}
} f[N], c[N];
int see(Face a, pon b)
{
	return ((b - A[a.v[0]]) & a.norm()) > 0;
}
db dist(Face a, pon b) //有向
{
	vec nor = a.norm();
	return (nor & (b - A[a.v[0]])) / dis(nor);
}

db area(Face a)
{
	return dis(a.norm()) / 2;
}
db volu(Face a)
{
	db d = dist(a, pon(0, 0, 0));
	return area(a) * d / 3;
}
int cnt = 0;
void Convex3()
{
	cnt = 0;
	f[++cnt] = Face(1, 2, 3);
	f[++cnt] = Face(3, 2, 1);
	for (int i = 4, cc = 0; i <= n; i++)
	{
		for (int j = 1, v; j <= cnt; j++)
		{
			if (!(v = see(f[j], A[i])))
				c[++cc] = f[j];
			for (int k = 0; k < 3; k++)
				vis[f[j].v[k]][f[j].v[(k + 1) % 3]] = v;
		}
		for (int j = 1; j <= cnt; j++)
		{
			for (int k = 0; k < 3; k++)
			{
				int x = f[j].v[k], y = f[j].v[(k + 1) % 3];
				if (vis[x][y] && !vis[y][x])
					c[++cc] = Face(x, y, i);
			}
		}
		for (int j = 1; j <= cc; j++)
			f[j] = c[j];
		cnt = cc, cc = 0;
	}
	return;
}
int main()
{
	srand(time(NULL));
	n = 1;
	while (scanf("%lf%lf%lf", &A[n].x, &A[n].y, &A[n].z) == 3)
		shake(A[n]), n++;
	n--;
	Convex3();
	return 0;
}

三维凸包