zoj 1453 Surround the Trees（凸包求周长）

  1 #include <stdio.h>
  2 #include <string.h>
  3 #include <stdlib.h>
  4 #include <iostream>
  5 #include <algorithm>
  6 #include <math.h>
  7 using namespace std;
  8 
  9 #define  MAX 110
 10 const double eps=1e-6;
 11 
 12 typedef struct
 13 {
 14     double x,y;
 15 }point;
 16 
 17 point c[MAX];
 18 
 19 bool dy(double x,double y)
 20 {
 21     return x>y+eps;
 22 }
 23 bool xy(double x,double y)
 24 {
 25     return x<y-eps;
 26 }
 27 bool xyd(double x,double y)
 28 {
 29     return x<y+eps;
 30 }
 31 bool dyd(double x,double y)
 32 {
 33     return x>y-eps;
 34 }
 35 bool dd(double x,double y)
 36 {
 37     return fabs(x-y)<eps;
 38 }
 39 
 40 double crossProduct(point a,point b,point c)
 41 {
 42     return (c.x-a.x)*(b.y-a.y)-(c.y-a.y)*(b.x-a.x);
 43 }
 44 double dist(point a,point b)
 45 {
 46     return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
 47 }
 48 
 49 bool cmp(point a,point b)
 50 {
 51     if(dd(a.y,b.y))
 52         return xy(a.x,b.x);
 53     return xy(a.y,b.y);
 54 }
 55 bool cmp1(point a,point b)
 56 {
 57     double len=crossProduct(c[0],a,b);
 58     if(dd(len,0.0))
 59         return xy(dist(c[0],a),dist(c[0],b));
 60     return xy(len,0.0);
 61 }
 62 
 63 point stk[MAX];
 64 int top;
 65 
 66 double dis()
 67 {
 68     double sum=0.0;
 69     for(int i=0;i<top;i++)
 70     {
 71         sum+=dist(stk[i],stk[i+1]);
 72     }
 73     sum+=dist(stk[top],stk[0]);
 74     return sum;
 75 }
 76 
 77 double Graham(int n)
 78 {
 79     sort(c,c+n,cmp);
 80     sort(c+1,c+n,cmp1);
 81     top=0;
 82     stk[top++]=c[0];
 83     stk[top++]=c[1];
 84     stk[top++]=c[2];
 85     top--;
 86     for(int i=3;i<n;i++)
 87     {
 88         while(1)
 89         {
 90             point a,b;
 91             a=stk[top];
 92             b=stk[top-1];
 93             if(xyd(crossProduct(a,b,c[i]),0.0))
 94             {
 95                 top--;
 96             }
 97             else
 98                 break;
 99         }
100         stk[++top]=c[i];
101     }
102     return dis();
103 }
104 
105 int main()
106 {
107     int i,j,k,t;
108     int n,m;
109     while(scanf("%d",&n)!=EOF&&n)
110     {
111         for(i=0;i<n;i++)
112         {
113             scanf("%lf%lf",&c[i].x,&c[i].y);
114         }
115         if(n==1)
116         {
117             printf("0.00\n");
118             //continue;
119         }
120         else if(n==2)
121         {
122             printf("%.2lf\n",2*dist(c[0],c[1]));
123             //continue;
124         }
125         else
126         {
127             printf("%.2lf\n",Graham(n));
128         }
129     }
130     return 0;
131 }