POJ 1113 Wall（Graham求凸包周长）

 1 #include <stdio.h>
 2 #include <string.h>
 3 #include <iostream>
 4 #include <cmath>
 5 #include <algorithm>
 6 
 7 const double PI = acos(-1.0) ;
 8 using namespace std ;
 9 
10 struct point
11 {
12     double x,y ;
13 }p[110],p1[110];
14 int n ,m;
15 
16 double dis(point a,point b)
17 {
18     return sqrt(double((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y))) ;
19 }
20 double cross(point a,point b,point c)
21 {
22     return (a.x-c.x)*(b.y-c.y) - (a.y-c.y)*(b.x-c.x) ;
23 }
24 bool cmp(point a,point b)
25 {
26     if(cross(a,b,p[0]) > 0 || cross(a,b,p[0]) == 0 && dis(a,p[0]) < dis(b,p[0]))
27         return true ;
28     return false ;
29 }
30 void Graham()
31 {
32     int cnt;
33     sort(p+1,p+n,cmp) ;
34     p[n] = p[0] ;
35     p1[0] = p[0] ;
36     p1[1] = p[1] ;
37     cnt = 1 ;
38     for(int i = 2 ; i <= n ; i++)
39     {
40         while(cnt >= 1 && cross(p1[cnt-1],p1[cnt],p[i]) <= 0) cnt -- ;
41         p1[ ++cnt] = p[i] ;
42     }
43     double sum = 0.0 ;
44     for(int i = 0 ; i < cnt ; i++)
45         {
46             sum += dis(p1[i],p1[i+1]) ;
47         }
48         printf("%.0lf\n",sum+2*PI*m) ;
49 }
50 int main()
51 {
52     while(~scanf("%d %d",&n,&m))
53     {
54         int pos = 0 ;
55         for(int i = 0 ; i < n ; i++)
56         {
57             scanf("%lf %lf",&p[i].x,&p[i].y) ;
58             if(p[pos].y > p[i].y || (p[pos].y == p[i].y && p[i].x < p[pos].x))
59                 pos = i ;
60         }
61 //        if(n == 1) {puts("0.00");continue ;}
62 //        if(n == 2)
63 //        {
64 //            printf("%.2lf\n",dis(p[1],p[0])) ;
65 //            continue ;
66 //        }
67         swap(p[pos],p[0]) ;
68         //printf("%d %d\n",p[0].x,p[0].y) ;
69         Graham() ;
70     }
71     return 0 ;
72 }