poj 3528 Ultimate Weapon (3D Convex Hull)

3528 -- Ultimate Weapon

　　一道三维凸包的题目，题目要求求出三维凸包的表面积。看懂了网上的三维凸包的代码以后，自己写的代码，跟网上的模板有所不同。调了一个晚上，结果发现错的只是数组开太小。_(:з」∠)_

代码如下：

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

 using namespace std;

 const double EPS = 1e-;
 const int N = ;
 inline int sgn(double x) { return (x > EPS) - (x < -EPS);}
 struct Point {
     double x, y, z;
     Point() {}
     Point(double x, double y, double z) : x(x), y(y), z(z) {}
     bool operator < (Point a) const {
         if (sgn(x - a.x)) return x < a.x;
         if (sgn(y - a.y)) return y < a.y;
         return z < a.z;
     }
     bool operator == (Point a) const { return !sgn(x - a.x) && !sgn(y - a.y) && !sgn(z - a.z);}
     Point operator + (Point a) { return Point(x + a.x, y + a.y, z + a.z);}
     Point operator - (Point a) { return Point(x - a.x, y - a.y, z - a.z);}
     Point operator * (double p) { return Point(x * p, y * p, z * p);}
     Point operator / (double p) { return Point(x / p, y / p, z / p);}
 } ;
 inline double dot(Point a, Point b) { return a.x * b.x + a.y * b.y + a.z * b.z;}
 inline double dot(Point o, Point a, Point b) { return dot(a - o, b - o);}
 inline Point cross(Point a, Point b) { return Point(a.y * b.z - a.z * b.y, a.z * b.x - a.x * b.z, a.x * b.y - a.y * b.x);}
 inline Point cross(Point o, Point a, Point b) { return cross(a - o, b - o);}
 inline double veclen(Point x) { return sqrt(dot(x, x));}
 inline double area(Point o, Point a, Point b) { return veclen(cross(a - o, b - o)) / 2.0;}
 // directed volume
 inline double volume(Point o, Point a, Point b, Point c) { return dot(cross(a - o, b - o), c - o);}

 struct _3DCH {
     Point pt[N];
     int pcnt;
     struct Face { // follow right-hand
         int a, b, c;
         bool ok;
         Face() {}
         Face(int a, int b, int c) : a(a), b(b), c(c) { ok = true;}
     } ;
     Face f[N << ];
     int fcnt, fid[N][N];
     bool outside(int p, int a, int b, int c) {
         int dir = sgn(volume(pt[a], pt[b], pt[c], pt[p]));
         return dir < ;
     }
     bool outside(int p, int x) { return outside(p, f[x].a, f[x].b, f[x].c);}
     void addface(int p, int a, int b, int c) {
         int dir = sgn(volume(pt[a], pt[b], pt[c], pt[p]));
         if (dir == ) return ;
         if (dir > ) {
             f[fcnt] = Face(a, b, c);
             fid[a][b] = fid[b][c] = fid[c][a] = fcnt++;
         } else {
             f[fcnt] = Face(c, b, a);
             fid[c][b] = fid[b][a] = fid[a][c] = fcnt++;
         }
     }
     bool dfs(int p, int x) {
         if (!f[x].ok) return true;
         if (outside(p, x)) {
             f[x].ok = false;
             if (!dfs(p, fid[f[x].b][f[x].a])) addface(f[x].c, f[x].b, f[x].a, p);
             if (!dfs(p, fid[f[x].c][f[x].b])) addface(f[x].a, f[x].c, f[x].b, p);
             if (!dfs(p, fid[f[x].a][f[x].c])) addface(f[x].b, f[x].a, f[x].c, p);
             return true;
         }
         return false;
     }
     bool build() {
         bool ok;
         fcnt = ;
         sort(pt, pt + pcnt);
         pcnt = unique(pt, pt + pcnt) - pt;
         ok = false;
         for (int i = ; i < pcnt; i++) {
             if (sgn(veclen(cross(pt[i], pt[], pt[])))) {
                 swap(pt[], pt[i]);
                 ok = true;
                 break;
             }
         }
         if (!ok) return false;
         ok = false;
         for (int i = ; i < pcnt; i++) {
             if (sgn(volume(pt[i], pt[], pt[], pt[]))) {
                 swap(pt[], pt[i]);
                 ok = true;
                 break;
             }
         }
         if (!ok) return false;
         addface(, , , );
         addface(, , , );
         addface(, , , );
         addface(, , , );
         for (int i = ; i < pcnt; i++) {
             for (int j = fcnt - ; j >= ; j--) {
                 if (f[j].ok && outside(i, j)) {
                     dfs(i, j);
                     break;
                 }
             }
         }
         int sz = fcnt;
         fcnt = ;
         for (int i = ; i < sz; i++) if (f[i].ok) f[fcnt++] = f[i];
         return true;
     }
     double vol() {
         Point O = Point(0.0, 0.0, 0.0);
         double ret = 0.0;
         for (int i = ; i < fcnt; i++) ret += volume(O, pt[f[i].a], pt[f[i].b], pt[f[i].c]);
         return fabs(ret) / 6.0;
     }
     double facearea() {
         double ret = 0.0;
         for (int i = ; i < fcnt; i++) ret += area(pt[f[i].a], pt[f[i].b], pt[f[i].c]);
         return ret;
     }
 } ch;

 int main() {
 //    freopen("in", "r", stdin);
     while (cin >> ch.pcnt) {
         for (int i = ; i < ch.pcnt; i++) scanf("%lf%lf%lf", &ch.pt[i].x, &ch.pt[i].y, &ch.pt[i].z);
         ch.build();
         printf("%.3f\n", ch.facearea());
 =    }
     return ;
 }

——written by Lyon