題目鏈接
https://www.luogu.org/problem/P2742
代碼
#include <bits/stdc++.h>
#define ll long long
using namespace std;
const ll maxn=1e4+10;
int inf=1e9;
void read(int &x){
int f=1;x=0;char s=getchar();
while(s<'0'||s>'9'){if(s=='-')f=-1;s=getchar();}
while(s>='0'&&s<='9'){x=x*10+s-'0';s=getchar();}
x*=f;
}
struct node{
double x,y;
};
node p[maxn],s[maxn];//s存儲凸包
double xx,yy; //極點
//向量ab,向量ac 叉積
double compare(node a,node b,node c){
return (b.x-a.x)*(c.y-a.y)-(c.x-a.x)*(b.y-a.y);
}
//極角排序
bool cmp(node a,node b){
node c;
c.x=xx;
c.y=yy;
if(compare(c,a,b)==0)
return a.x<b.x;
else
return compare(c,a,b)>0;
}
//求邊長
double bian(node a,node b){
return sqrt((a.x-b.x)*(a.x-b.x)+(b.y-a.y)*(b.y-a.y));
}
int n;
void tubao(){
int k,top=1;
yy=inf;
for(int i=0;i<n;i++){
if(yy>p[i].y){
yy=p[i].y;
xx=p[i].x;
k=i;
}
}
p[k]=p[0];
sort(p+1,p+n,cmp);
s[0].x=xx;
s[0].y=yy;
s[1]=p[1];
for(int i=2;i<n;){
if(top&&(compare(s[top-1],s[top],p[i])<0))
top--;
else
s[++top]=p[i++];
}
/*
double ans1=0;
for(int i=0;i<=top;i++) //遍歷求構成三角形最大的面積
for(int j=i+1;j<=top;j++)
for(int k=j+1;k<=top;k++)
ans1=max(ans1,compare(s[j],s[k],s[i]));
printf("%.2lf\n",0.5*ans1);
*/
double ans[maxn]; // 求凸多邊形周長
s[++top]=s[0];
for(int i=0; i<top; i++)
ans[i]=bian(s[i],s[i+1]);
double sum=0;
for(int i=0; i<top; i++){
sum+=ans[i];
}
printf("%.2lf\n",sum);
}
int main(){
int i;
read(n);
for(i=0;i<n;i++){
scanf("%lf%lf",&p[i].x,&p[i].y);
}
tubao();
return 0;
}