poj 2451 Uyuw's Concert （半平面交）

2451 -- Uyuw's Concert

　　继续半平面交，这还是简单的半平面交求面积，不过输入用cin超时了一次。

代码如下：

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

 using namespace std;

 struct Point {
     double x, y;
     Point() {}
     Point(double x, double y) : x(x), y(y) {}
 } ;
 template<class T> T sqr(T x) { return x * x;}
 typedef Point Vec;
 Vec operator + (Vec a, Vec b) { return Vec(a.x + b.x, a.y + b.y);}
 Vec operator - (Vec a, Vec b) { return Vec(a.x - b.x, a.y - b.y);}
 Vec operator * (Vec a, double p) { return Vec(a.x * p, a.y * p);}
 Vec operator / (Vec a, double p) { return Vec(a.x / p, a.y / p);}

 const double EPS = 1e-;
 const double PI = acos(-1.0);
 inline int sgn(double x) { return (x > EPS) - (x < -EPS);}

 inline double dotDet(Vec a, Vec b) { return a.x * b.x + a.y * b.y;}
 inline double crossDet(Vec a, Vec b) { return a.x * b.y - a.y * b.x;}
 inline double dotDet(Point o, Point a, Point b) { return dotDet(a - o, b - o);}
 inline double crossDet(Point o, Point a, Point b) { return crossDet(a - o, b - o);}
 inline double vecLen(Vec x) { return sqrt(dotDet(x, x));}
 inline double toRad(double deg) { return deg / 180.0 * PI;}
 inline double angle(Vec v) { return atan2(v.y, v.x);}
 inline Vec vecUnit(Vec x) { return x / vecLen(x);}
 inline Vec normal(Vec x) { return Vec(-x.y, x.x) / vecLen(x);}

 const int N = ;
 struct DLine {
     Point p;
     Vec v;
     double ang;
     DLine() {}
     DLine(Point p, Vec v) : p(p), v(v) { ang = atan2(v.y, v.x);}
     bool operator < (DLine L) const { return ang < L.ang;}
 } dl[N];

 inline bool onLeft(DLine L, Point p) { return crossDet(L.v, p - L.p) > ;}
 Point dLineIntersect(DLine a, DLine b) {
     Vec u = a.p - b.p;
     double t = crossDet(b.v, u) / crossDet(a.v, b.v);
     return a.p + a.v * t;
 }

 struct Poly {
     vector<Point> pt;
     Poly() { pt.clear();}
     ~Poly() {}
     Poly(vector<Point> &pt) : pt(pt) {}
     Point operator [] (int x) { return pt[x];}
     int size() { return pt.size();}
     double area() {
         double ret = 0.0;
         int sz = pt.size();
         pt.push_back(pt[]);
         for (int i = ; i <= sz; i++) ret += crossDet(pt[i], pt[i - ]);
         pt.pop_back();
         return fabs(ret / 2.0);
     }
 } ;

 Poly halfPlane(DLine *L, int n) {
     Poly ret = Poly();
     sort(L, L + n);
     int fi, la;
     Point *p = new Point[n];
     DLine *q = new DLine[n];
     q[fi = la = ] = L[];
     for (int i = ; i < n; i++) {
         while (fi < la && !onLeft(L[i], p[la - ])) la--;
         while (fi < la && !onLeft(L[i], p[fi])) fi++;
         q[++la] = L[i];
         if (sgn(crossDet(q[la].v, q[la - ].v)) == ) {
             la--;
             if (onLeft(q[la], L[i].p)) q[la] = L[i];
         }
         if (fi < la) p[la - ] = dLineIntersect(q[la - ], q[la]);
     }
     while (fi < la && !onLeft(q[fi], p[la - ])) la--;
     if (la < fi) return ret;
     p[la] = dLineIntersect(q[la], q[fi]);
     for (int i = fi; i <= la; i++) ret.pt.push_back(p[i]);
     return ret;
 }

 const int dir[][] = { {, }, {, }, {, }, {, }};

 int main() {
     int T, n;
     while (~scanf("%d", &n)) {
         Point x[];
         for (int i = ; i < n; i++) {
             for (int j = ; j < ; j++) {
                 scanf("%lf%lf", &x[j].x, &x[j].y);
             }
             dl[i] = DLine(x[], x[] - x[]);
         }
         for (int i = ; i < ; i++) {
             dl[n + i] = DLine(Point(10000.0 * dir[i][], 10000.0 * dir[i][]),
                               Point(10000.0 * dir[(i + ) & ][], 10000.0 * dir[(i + ) & ][]) - Point(10000.0 * dir[i][], 10000.0 * dir[i][]));
         }
         Poly tmp = halfPlane(dl, n + );
         printf("%.1f\n", tmp.area());
     }
     return ;
 }

——written by Lyon