poj1113 凸包入門題

計算凸包周長和一個圓的周長

#include<iostream>
#include<stdio.h>
#include<string.h>
#include<string>
#include<stdlib.h>
#include<cmath>
#include<queue>
#include<algorithm>
using namespace std;
#define rd(x) scanf("%d",&x)
#define rdd(x,y) scanf("%d%d",&x,&y)
#define rddd(x,y,z) scanf("%d%d%d",&x,&y,&z)
#define rdddd(x,y,z,w) scanf("%d%d%d%d",&x,&y,&z,&w)
#define rds(s) scanf("%s",s)
#define rep(i,n) for(int i=0;i<n;i++)
#define LL long long
const int N = 1e5+10;
const int M=2000;
const int inf=0x3f3f3f3f;
const double eps=1e-9;
int MOD=1e9+7;
int cas=1;
int n,m,k,q,L;
int sgn(double x){return x<-eps?-1:x<eps?0:1;}
struct Point{
    double x,y;
    Point(){}
    Point(double _x,double _y){
        x=_x;y=_y;
    }
};
double cross(Point a,Point b,Point c){
    return (b.x-a.x)*(c.y-a.y)-(b.y-a.y)*(c.x-a.x);
}
bool same(Point a,Point b){
    if(sgn(a.x-b.x)==0 && sgn(a.y-b.y)==0) return true;
    return false;
}

double dist(Point a,Point b){
    return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
}
Point p[1005],convex[1005];
int mi;
bool cmp(Point a,Point b){
    int ret=sgn(cross(p[0],a,b));
    if(ret==0) return dist(p[0],a)<dist(p[0],b);
    return ret>0;
}
int graham(){
    int top=0;
    convex[top++]=p[0];
    convex[top++]=p[1];
    int k=2;
    while(k<=n){
        while(top>=2 && sgn(cross(convex[top-2],p[k%n],convex[top-1]))>=0) top--;
        convex[top++]=p[k%n];
        k++;
    }
    return top;
}
double pi=acos(-1.0);
int main()
{
#ifndef ONLINE_JUDGE
freopen("aaa","r",stdin);
#endif
    int T;
    rdd(n,L);
    mi=1;
    for(int i=0;i<n;i++){
        scanf("%lf%lf",&p[i].x,&p[i].y);
        if(sgn(p[mi].y-p[i].y)>0 || sgn(p[mi].y-p[i].y)==0  && sgn(p[mi].x-p[i].x)>0) mi=i;
    }
    swap(p[0],p[mi]);
    sort(p+1,p+n,cmp);
  //  }
    int num=graham();
    double ans=0;
    for(int i=1;i<num;i++){
        ans+=dist(convex[i-1],convex[i]);
    }
    ans+=2*pi*L;
    printf("%.0f\n",ans);
    return 0;
}