poj2451Uyuw's Concert(半平面交）

链接

逆时针给出线段，如果模板是顺时针的修改下系数的符号进行平面交即可。

  1 #include <iostream>

  2 #include<cstdio>

  3 #include<cstring>

  4 #include<algorithm>

  5 #include<stdlib.h>

  6 #include<vector>

  7 #include<cmath>

  8 #include<queue>

  9 #include<set>

 10 using namespace std;

 11 #define N 20100

 12 #define LL long long

 13 #define INF 0xfffffff

 14 const double eps = 1e-8;

 15 const double pi = acos(-1.0);

 16 const double inf = ~0u>>2;

 17 int m;

 18 int cCnt,curCnt;

 19 struct point

 20 {

 21     double x,y;

 22     point(double x=0,double y =0 ):x(x),y(y) {}

 23 };

 24 point points[N],p[N],q[N];

 25 void getline(point x,point y,double &a,double &b,double   &c)

 26 {

 27     a = x.y - y.y;

 28     b = y.x - x.x;

 29     c = x.x * y.y-y.x * x.y;

 30 }

 31 void initial()

 32 {

 33     for(int i = 1; i <= m; ++i)p[i] = points[i];

 34     p[m+1] = p[1];

 35     p[0] = p[m];

 36     cCnt = m;

 37 }

 38 point intersect(point x,point y,double a,double b,double c)

 39 {

 40     double u = fabs(a * x.x + b * x.y + c);

 41     double v = fabs(a * y.x + b * y.y + c);

 42     point pt;

 43     pt.x=(x.x * v + y.x * u) / (u + v);

 44     pt.y=(x.y * v + y.y * u) / (u + v);

 45     return  pt;

 46 }

 47 void cut(double a,double b ,double c)

 48 {

 49     curCnt = 0;

 50     for(int i = 1; i <= cCnt; ++i)

 51     {

 52         if(a*p[i].x + b*p[i].y + c >= 0)q[++curCnt] = p[i];

 53         else

 54         {

 55             if(a*p[i-1].x + b*p[i-1].y + c > 0)

 56                 q[++curCnt] = intersect(p[i],p[i-1],a,b,c);

 57             if(a*p[i+1].x + b*p[i+1].y + c > 0)

 58                 q[++curCnt] = intersect(p[i],p[i+1],a,b,c);

 59         }

 60     }

 61     for(int i = 1; i <= curCnt; ++i)p[i] = q[i];

 62     p[curCnt+1] = q[1];

 63     p[0] = p[curCnt];

 64     cCnt = curCnt;

 65 }

 66 void solve()

 67 {

 68     double area = 0;

 69     for(int i = 1; i <= cCnt; ++i)

 70         area += p[i].x * p[i + 1].y - p[i + 1].x * p[i].y;

 71     area = fabs(area / 2.0);

 72     printf("%.1f\n",area);

 73 

 74 }

 75 void GuiZhengHua()

 76 {

 77     //规整化方向，逆时针变顺时针，顺时针变逆时针

 78     for(int i = 1; i < (m+1)/2; i ++)

 79         swap(points[i], points[m-i]);

 80 }

 81 int main()

 82 {

 83     points[1] = point(0,0);

 84     points[4] = point(0,10000);

 85     points[3] = point(10000,10000);

 86     points[2] = point(10000,0);

 87     points[5] = p[1];

 88     int n,i;

 89     while(scanf("%d",&n)!=EOF)

 90     {

 91         m = 4;

 92         initial();

 93         for(i = 1; i <= 4; ++i)

 94         {

 95             double a,b,c;

 96             getline(points[i],points[i+1],a,b,c);

 97             cut(a,b,c);

 98         }

 99         for(i = 1 ; i <= 2*n ; i+=2)

100         {

101             point p1,p2;

102             scanf("%lf%lf%lf%lf",&p1.x,&p1.y,&p2.x,&p2.y);

103             double a,b,c;

104             getline(p1,p2,a,b,c);

105             cut(a,b,c);

106         }

107 

108        // m = 2*n+4;

109         //GuiZhengHua();

110         //points[m+1] = points[1];

111         solve();

112     }

113     return 0;

114 }

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