POJ 3348 Cows

大概题意：n棵树，围篱笆，如果使得面积最大。

题解：凸包，再求面积，面积除以100即可

代码：

 1 #include <iostream>
 2 #include <cstdlib>
 3 #include <cstdio>
 4 #include <cstring>
 5 #include <algorithm>
 6 #include <queue>
 7 #include <cmath>
 8 using namespace std;
 9 const double eps = 1E-8;
10 struct POINT{
11         double x,y;
12         POINT( double a = 0, double b = 0 ){ x = a; y = b; }
13 };
14 POINT pointset[10000+50];
15 POINT ch[100000+50];
16 double multiply(POINT sp, POINT ep, POINT op)
17 {
18         return (sp.x - op.x)*(ep.y - op.y) - ( sp.y - op.y )*( ep.x - op.x );
19 }
20 double dist(POINT p1,POINT p2)
21 {
22         return sqrt( (p1.x - p2.x)*(p1.x - p2.x) + ( p1.y - p2.y )*( p1.y - p2.y ) );
23 }
24 double area_of_polygon( int vcount,POINT ch[] )
25 {
26         if(vcount<3) return 0;
27         double s;
28         s = ch[0].y*(ch[vcount-1].x-ch[1].x);
29         for(int i = 1;i < vcount ; i++)
30                 s+=ch[i].y*(ch[i-1].x-ch[(i+1)%vcount].x);
31         return s/2;
32 }
33 void Graham_scan(POINT pointset[],POINT ch[],int n,int &len)
34 {
35         int k=0,top=2;
36         POINT tmp;
37         for(int i = 1; i < n; i++ )
38                 if(pointset[i].y<pointset[k].y || ( pointset[i].y == pointset[k].y ) &&
39                 pointset[i].x<pointset[k].x) k = i;
40         tmp = pointset[0];
41         pointset[0] = pointset[k];
42         pointset[k] = tmp;
43         for(int i = 1;i < n;i++)
44         {
45                 k = i;
46                 for(int j = i+1; j < n; j++)
47                         if(multiply(pointset[j],pointset[k],pointset[0])>0||
48                         (multiply(pointset[j],pointset[k],pointset[0])==0&&
49                         dist(pointset[0],pointset[k])-dist(pointset[0],pointset[j])>eps))
50                         k=j;
51                 tmp = pointset[i];
52                 pointset[i] = pointset[k];
53                 pointset[k] = tmp;
54         }
55         ch[0] = pointset[0];
56         ch[1] = pointset[1];
57         ch[2] = pointset[2];
58         for(int i = 3;i < n; i++)
59         {
60                 while(multiply(pointset[i],ch[top],ch[top-1])>=0)
61                         top--;
62                 ch[++top] = pointset[i];
63         }
64         len = top + 1;
65 }
66 int main()
67 {
68         int n;
69        cin>>n;
70        for(int i = 0; i < n; i++)
71                scanf("%lf%lf",&pointset[i].x,&pointset[i].y);
72         int len;
73         Graham_scan(pointset,ch,n,len);
74         double s = area_of_polygon(len,ch);
75         int ss = s/50;
76         cout<<ss<<endl;
77 }
View Code

 

posted on 2015-08-22 22:07  小松song  阅读(122)  评论(0)    收藏  举报

导航