ecnu1624求交集多边形面积

  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 10000
 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 struct point
 18 {
 19     double x,y;
 20     point(double x=0,double y =0 ):x(x),y(y) {}
 21 } p[N],q[N],ch[N],chh[N];
 22 typedef point pointt;
 23 point operator -(point a,point b)
 24 {
 25     return point(a.x-b.x,a.y-b.y);
 26 }
 27 int dcmp(double x)
 28 {
 29     if(fabs(x)<eps) return 0;
 30     return x<0?-1:1;
 31 }
 32 double cross(point a,point b)
 33 {
 34     return a.x*b.y-a.y*b.x;
 35 }
 36 double dis(point a)
 37 {
 38     return sqrt(a.x*a.x+a.y*a.y);
 39 }
 40 double getarea(point p[],int n)
 41 {
 42     int i;
 43     double area = 0;
 44     for(i =0  ; i < n-1; i++)
 45         area+=cross(p[i]-p[0],p[i+1]-p[0]);
 46     area = fabs(area)/2;
 47     return area;
 48 }
 49 bool PtInPolygon (point p, point ptPolygon[], int nCount)
 50 {
 51     int i,nCross = 0;
 52     for(i =0 ; i< nCount ; i++)
 53     {
 54         point p1 = ptPolygon[i];
 55         point p2 = ptPolygon[(i+1)%nCount];
 56         if(dcmp(p1.y-p2.y)==0) continue;
 57         if(dcmp(p.y-min(p1.y,p2.y))<0) continue;
 58         if(dcmp(p.y-max(p1.y,p2.y))>=0) continue;
 59         double x = (double)(p.y-p1.y)*(double)(p2.x-p1.x)/(double)(p2.y-p1.y)+p1.x;
 60         if(x>p.x)   nCross++;
 61     }
 62     return (nCross % 2 == 1);
 63 }
 64 bool segprointer(point a1,point a2,point b1,point b2)
 65 {
 66     double c1 = cross(a2-a1,b1-a1),c2 = cross(a2-a1,b2-a1);
 67     double c3 = cross(b2-b1,a1-b1),c4 = cross(b2-b1,a2-b1);
 68     return dcmp(c1)*dcmp(c2)<0&&dcmp(c3)*dcmp(c4)<0;
 69 }
 70 bool intersection1(point p1, point p2, point p3, point p4, point& p)      // 直线相交
 71 {
 72     double a1, b1, c1, a2, b2, c2, d;
 73     a1 = p1.y - p2.y;
 74     b1 = p2.x - p1.x;
 75     c1 = p1.x*p2.y - p2.x*p1.y;
 76     a2 = p3.y - p4.y;
 77     b2 = p4.x - p3.x;
 78     c2 = p3.x*p4.y - p4.x*p3.y;
 79     d = a1*b2 - a2*b1;
 80     if (!dcmp(d))    return false;
 81     p.x = (-c1*b2 + c2*b1) / d;
 82     p.y = (-a1*c2 + a2*c1) / d;
 83     return true;
 84 }
 85 double mul(point p0,point p1,point p2)
 86 {
 87     return cross(p1-p0,p2-p0);
 88 }
 89  
 90 bool cmp(point a,point b)
 91 {
 92     if(dcmp(mul(ch[0],a,b))==0)
 93         return dis(a-ch[0])<dis(b-p[0]);
 94     else
 95         return dcmp(mul(ch[0],a,b))>0;
 96 }
 97 bool cmpp(point a,point b)
 98 {
 99     if(dcmp(a.x-b.x)==0) return a.y<b.y;
100     return a.x<b.x;
101 }
102 int main()
103 {
104     int n,m,i,j;
105     while(scanf("%d",&n)!=EOF)
106     {
107  
108         for(i = 0; i < n ; i++)
109             scanf("%lf%lf",&p[i].x,&p[i].y);
110         p[n] = p[0];
111         scanf("%d",&m);
112         for(i = 0; i < m; i++)
113             scanf("%lf%lf",&q[i].x,&q[i].y);
114         q[m] = q[0];
115         int g = 0;
116         for(i = 0; i < n ; i ++)
117         {
118             if(PtInPolygon(p[i],q,m))
119                 ch[g++] = p[i];
120         }
121         for(i = 0; i < m ; i ++)
122         {
123             if(PtInPolygon(q[i],p,n))
124                 ch[g++] = q[i];
125         }
126         for(i = 0 ; i < n;  i++)
127         {
128             for(j = 0; j < m ; j++)
129             {
130                 if(segprointer(p[i],p[i+1],q[j],q[j+1])==0) continue;
131                 point pp;
132                 if(!intersection1(p[i],p[i+1],q[j],q[j+1],pp))continue;
133                 ch[g++] = pp;
134             }
135         }
136         double ans = 0;//getarea(p,n)+getarea(q,m);
137         if(g==0)
138             ans = 0;
139         else
140         {
141             int k = 0,o=0;
142             sort(ch,ch+g,cmpp);
143             chh[o++] = ch[0];
144             for(i  = 1; i < g; i++)
145             if(dcmp(ch[i].x-ch[i-1].x)==0&&dcmp(ch[i].y-ch[i-1].y)==0)
146             continue;
147             else chh[o++] = ch[i];
148             g = o;
149             for(i = 1; i < g ; i ++)
150             {
151                 if(dcmp(chh[i].y-chh[k].y)<0||(dcmp(chh[i].y-chh[k].y)==0&&dcmp(chh[i].x-chh[k].x)<0))
152                     k = i;
153             }
154             if(k!=0) swap(chh[k],chh[0]);
155             sort(chh+1,chh+g,cmp);
156             ans = getarea(chh,g);
157         }
158         printf("%.2f\n",ans);
159     }
160     return 0;
161 }