## Solución al problema número 218 de UVA - 218.

Cualquier duda no dudes en contactar.

``````#include <bits/stdc++.h>
#define INF 0x3f3f3f3f
#define EPS 1e-9
#define PI acos(-1.0)
using namespace std;

struct point{
double x,y;
point(){x=y=0;}
point(double _x,double _y){x=_x,y=_y;}
bool operator <(point other) const{
if (fabs(x-other.x)>EPS)return x<other.x;
return y<other.y;
}bool operator ==(point other) const{
return (fabs(x-other.x)<EPS)&&
(fabs(y-other.y)<EPS);
}
point operator +(point other) const{
return point(x+other.x,y+other.y);
}point operator -(point other) const{
return point(x-other.x,y-other.y);
}
};

double dist(point p1, point p2) {
return hypot(p1.x - p2.x, p1.y - p2.y); }

double perimeter(const vector<point> &P) {
double result = 0.0;
for (int i = 0; i < (int)P.size()-1; i++)
result += dist(P[i], P[i+1]);
return result; }

double cross(point o, point a, point b) {
return (a.x-o.x)*(b.y-o.y) - (a.y-o.y)*(b.x-o.x);
}

vector<point> CH(vector<point> P){
vector<point> res;
sort(P.begin(),P.end());
int n = P.size();
int m=0;
for (int i=0;i<n;i++){
while (m>1&&cross(res[m-2], res[m-1], P[i]) <= 0)res.pop_back(),m--;
res.push_back(P[i]),m++;
}
for (int i = n-1, t = m+1; i >= 0; i--) {
while (m>=t&&cross(res[m-2], res[m-1], P[i]) <= 0)res.pop_back(),m--;
res.push_back(P[i]),m++;
}
return res;
}

int main()
{
int c = 1,n;
while(scanf("%d",&n)==1 && n!=0)
{
if(c!=1) printf("\n");
vector<point> P;
double x,y;
for(int i=0; i<n;i++)
{
scanf("%lf%lf",&x,&y);
P.push_back(point(x, y));
}
P = CH(P);
reverse(P.begin(),P.end());
printf("Region #%d:\n",c++);
for(unsigned int i = 0; i<P.size(); i++)
{
//printf("PUNTO(%3.lf,%.3lf)",P[i].x,P[i].y);
if(i==0) printf("(%.1lf,%.1lf)",P[i].x,P[i].y);
else printf("-(%.1lf,%.1lf)",P[i].x,P[i].y);
}
if(P.size()==1) printf("-(%.1lf,%.1lf)",round(P[0].x*10)/10,round(P[0].y*10)/10);
printf("\nPerimeter length = %.2lf\n",perimeter(P));
}
return 0;
}
``````