Wall(凸包)

http://poj.org/problem?id=1113

题意：给出一些点的坐标，和一个半径r，求出这些点围成的凸包的周长再加上一个半径为r的圆的周长。

 1 #include <stdio.h>
 2 #include <algorithm>
 3 #include <math.h>
 4 const double PI=acos(-1.0);
 5 const int N=1002;
 6 using namespace std;
 7 
 8 struct Point
 9 {
10     double x;
11     double y;
12     Point (double x = 0,double y = 0):x(x),y(y) {}
13     bool friend operator < (const Point &a, const Point &b)
14     {
15         return a.x < b.x||(a.x==b.x&&a.y < b.y);
16     }
17 } p[N],c[N];
18 typedef Point Vector;
19 double dis(Point A,Point B)//两点间的距离
20 {
21     return sqrt((A.x-B.x)*(A.x-B.x)+(A.y-B.y)*(A.y-B.y));
22 }
23 Vector operator- (Point A,Point B)//求向量
24 {
25     return Vector(B.x-A.x,B.y-A.y);
26 }
27 double Cross(Vector A,Vector B)//求叉积
28 {
29     return A.x*B.y-A.y*B.x;
30 }
31 int ConvexHull(Point *p,int n,Point *c)//计算凸包
32 {
33     int k = 0;
34     for (int i = 0; i < n; i++)
35     {
36         while(k > 1 && Cross(c[k-2]-c[k-1],c[k-2]-p[i])<=0)
37             k--;
38         c[k++] = p[i];
39 
40     }
41     int m = k;
42     for (int i = n-2; i >= 0; i--)
43     {
44         while(k > m && Cross(c[k-2]-c[k-1],c[k-2]-p[i])<=0)
45             k--;
46         c[k++] = p[i];
47     }
48     c[k] = c[0];
49     return k;
50 }
51 
52 int main()
53 {
54     int n;
55     double r;
56     scanf("%d %lf",&n,&r);
57     for (int i = 0; i < n; i++)
58         scanf("%lf %lf",&p[i].x,&p[i].y);
59     sort(p,p+n);
60     int cnt = ConvexHull(p,n,c);
61     double len = 0;
62     for (int i = 1; i <= cnt; i++)
63     {
64         len+=dis(c[i],c[i-1]);
65     }
66     len+=2*PI*r;
67     printf("%.0f",len);
68     return 0;
69 }
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posted @ 2013-10-25 21:06  N_ll  阅读(269)  评论(0)  编辑  收藏  举报