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LA 4127 - The Sky is the Limit (离散化 扫描线 几何模板)

题目链接

非原创 原创地址:http://blog.csdn.net/jingqi814/article/details/26117241

题意:输入n座山的信息(山的横坐标,高度,山底宽度),计算他们的轮廓线,

即露出来的表面边长,有些山是重叠的不计。空白地带不计,每座山都是等腰三角形。

分析:大白书P414页。

求小山的总长度,用一些虚线将其离散化,分成一段一段的,特征点:山脚,山顶,交点。这样就能保

证相邻两个扫描点之间再无交点。然后一最上面的点就是分割点,维护上一个点lastp即可。

  1 #include<iostream>  2 #include<cmath>  3 #include<cstdio>  4 #include<algorithm>  5 #include<vector>  6 const double eps=1e-8;  7 using namespace std;  8   9 struct Point{    //定义点 10     double x; 11     double y; 12     Point(double x=0,double y=0):x(x),y(y){}   //构造函数 13     //void operator<<(Point &A) {cout<<A.x<<‘ ‘<<A.y<<endl;} 14 }; 15  16 int dcmp(double x)  {return (x>eps)-(x<-eps); }   //判断精度 17  18 typedef  Point  Vector;    //自定义别名 19  20 Vector  operator +(Vector A,Vector B) { return Vector(A.x+B.x,A.y+B.y);} //向量+向量=向量,点+向量=点 21  22 Vector  operator -(Vector A,Vector B) { return Vector(A.x-B.x,A.y-B.y); }  //点-点=向量 23  24 Vector  operator *(Vector A,double p) { return Vector(A.x*p,A.y*p);  }   //向量*数=向量 25  26 Vector  operator /(Vector A,double p) {return Vector(A.x/p,A.y/p);}    //向量/数=向量 27  28 ostream &operator<<(ostream & out,Point & P) { out<<P.x<< <<P.y<<endl; return out;}  //输出点的 符号重载 29  30 bool  operator< (const Point &A,const Point &B) { return A.x<B.x||(A.x==B.x&&A.y<B.y); }  //小于号 重载 31  32 bool  operator== ( const Point &A,const Point &B) { return dcmp(A.x-B.x)==0&&dcmp(A.y-B.y)==0;}  //等于号 重载 33  34 double  Dot(Vector A,Vector B) {return A.x*B.x+A.y*B.y;}  //点积 35  36 double  Cross(Vector A,Vector B)  {return A.x*B.y-B.x*A.y; } //叉积 37  38 double  Length(Vector A)  { return sqrt(Dot(A, A));}  //向量长度 39  40 double  Angle(Vector A,Vector B) {return acos(Dot(A,B)/Length(A)/Length(B));}  //向量夹角 41  42 double  Area2(Point A,Point B,Point C ) {return Cross(B-A, C-A);}  //三角形面积 43  44 Vector Rotate(Vector A,double rad) { return Vector(A.x*cos(rad)-A.y*sin(rad),A.x*sin(rad)+A.y*cos(rad));} //向量旋转,rad为逆时针旋转的弧度 45 Vector Normal(Vector A) {double L=Length(A);return Vector(-A.y/L,A.x/L);}  //计算向量的单位法线,需确保A不是零向量。 46  47 Point GetLineIntersection(Point P,Vector v,Point Q,Vector w)  //两直线的交点。需确保直线 P+tv 和 Q+tw有唯一交点,cross(v,w)需非0。 48 {                                                             //t是参数,v,w分别为两直线的向量。 49     Vector u=P-Q; 50     double t=Cross(w, u)/Cross(v,w); 51     return P+v*t; 52 } 53  54 double DistanceToLine(Point P,Point A,Point B)  //点到直线的距离,p到ab的距离 55 { 56     Vector v1=P-A; Vector v2=B-A; 57     return fabs(Cross(v1,v2))/Length(v2); 58 } 59  60 double DistanceToSegment(Point P,Point A,Point B)  //点到线段的距离,p到ab 61 { 62     if(A==B)  return Length(P-A); 63     Vector v1=B-A; 64     Vector v2=P-A; 65     Vector v3=P-B; 66  67     if(dcmp(Dot(v1,v2))==-1)    return  Length(v2); 68     else if(Dot(v1,v3)>0)    return Length(v3); 69     else return DistanceToLine(P, A, B); 70  71 } 72  73 Point GetLineProjection(Point P,Point A,Point B)  //点在直线的投影,p到ab 74 { 75     Vector v=B-A; 76     Vector v1=P-A; 77     double t=Dot(v,v1)/Dot(v,v); 78     return  A+v*t; 79 } 80  81 bool  SegmentProperIntersection(Point a1,Point a2,Point b1,Point b2)  //判断线段相交,交点不在端点上(如果交点在端点上可以借助下面的OnSegment来判断) 82 { 83     double c1=Cross(b1-a1, a2-a1); 84     double c2=Cross(b2-a1, a2-a1); 85     double c3=Cross(a1-b1, b2-b1); 86     double c4=Cross(a2-b1, b2-b1); 87     return dcmp(c1)*dcmp(c2)<0&&dcmp(c3)*dcmp(c4)<0 ; 88 } 89  90 bool  OnSegment(Point P,Point A,Point B)  //判断一个点是否在一条线段上 91 { 92     return dcmp(Cross(P-A, P-B))==0&&dcmp(Dot(P-A,P-B))<0; 93 } 94  95 double PolygonArea(Point *p,int n)  //多边形的有向面积 96 { 97     double area=0; 98  99     for(int i=1;i<n-1;i++)100     {101         area+=Cross(p[i]-p[0], p[i+1]-p[0]);102     }103     return area/2;104 105 }106 107 Point  read_point()   //输入点108 {109     Point P;110     scanf("%lf%lf",&P.x,&P.y);111     return  P;112 }113 114 int n;115 Point L[110][2][2];116 double x[20000];   //  存放离散化的x坐标117 118 int main()119 {120     double X,H,B;121     int cas=0;122     while(cin>>n && n)123     {124         int c=0;125         for(int i=0;i<n;i++)126         {127             scanf("%lf%lf%lf",&X,&H,&B);128             L[i][0][0]=Point(X-B*0.5,0);129             L[i][0][1]=L[i][1][0]=Point(X,H);130             L[i][1][1]=Point(X+B*0.5,0);131 132             x[c++]=X-B*0.5;133             x[c++]=X;134             x[c++]=X+B*0.5;135         }136             for(int i=0;i<n;i++)137                 for(int a=0;a<2;a++)138                     for(int j=i+1;j<n;j++)139                         for(int b=0;b<2;b++)140                         {141                             Point A=L[i][a][0];142                             Point B=L[i][a][1];143                             Point C=L[j][b][0];144                             Point D=L[j][b][1];145 146                             if(SegmentProperIntersection(A, B, C, D))147                             {148                                 x[c++]=GetLineIntersection(A, B-A, C, D-C).x;149                             }150                         }151 152         sort(x,x+c);153         c=unique(x, x+c)-x; //unique()函数去重函数,在头文件algorithm中154         double ans=0;155         Point lastp=Point(x[0],0);156 157         for(int i=0;i<c;i++)158         {159             Point P=Point(x[i],0);160             Vector v=Vector(0,1);161             double maxy=-1;162             Point inter;163 164             for(int j=0;j<n;j++)165                 for(int a=0;a<2;a++)166                 {167                     Point A=L[j][a][0];168                     Point B=L[j][a][1];169                     if(dcmp(A.x-x[i])<=0&&dcmp(B.x-x[i])>=0)170                     {171                         inter=GetLineIntersection(A, B-A, P, v);172                         maxy=max(maxy,inter.y);173                     }174                 }175             if(i>0&&(dcmp(maxy)>0||dcmp(lastp.y)>0))   ans+=Length(Point(x[i],maxy)-lastp);176             lastp=Point(x[i],maxy);177         }178         printf("Case %d: %.0f\n\n",++cas,ans);179     }180 }