OJ-Problems-Source/HDOJ/1392_autoAC.cpp

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2016-08-13 23:51:27 +08:00
#include<cstdio>
#include<cmath>
#include<algorithm>
using namespace std;
struct node
{
int x,y;
}a[110],stack1[110];
double distan(node a,node b)
{
return (double)sqrt((a.x-b.x)*(a.x-b.x)*1.0+(a.y-b.y)*(a.y-b.y)*1.0);
}
double across(node a,node n1,node n2)
{
return (n1.x-a.x)*(n2.y-a.y) - (n1.y-a.y)*(n2.x-a.x);
}
bool cmp(node a1,node b1)
{
double k=across(a[0],a1,b1);
if(k>0) return true;
else if (k==0&&distan(a[0],a1)<distan(a[0],b1))
{
return true;
}
else return false;
}
void anglesort(int n)
{
int i,k=0;
node temp;
for(i=1;i<n;i++)
{
if(a[i].y<a[k].y||(a[i].y==a[k].y&&a[i].x<a[k].x))
k=i;
}
temp=a[0];
a[0]=a[k];
a[k]=temp;
sort(a+1,a+n,cmp);
}
void Graham(int n)
{
anglesort(n);
int i,head;
double sum=0;
a[n]=a[0];
stack1[0]=a[0];
stack1[1]=a[1];
stack1[2]=a[2];
head=2;
for(i=3;i<=n;i++)
{
while(head>=2 && (across(stack1[head-1],stack1[head],a[i])<=0)) head--;
stack1[++head]=a[i];
}
for(i=0;i<head;i++)
{
sum+=distan(stack1[i],stack1[i+1]);
}
printf("%.2lf\n",sum);
}
int main()
{
int i,n;
while(scanf("%d",&n),n)
{
for(i=0;i<n;i++)
{
scanf("%d%d",&a[i].x,&a[i].y);
}
if(n==1)
{
printf("0.00\n");
continue;
}
if(n==2)
{
printf("%.2lf\n",distan(a[0],a[1]));
continue;
}
Graham(n);
}
return 0;
}