hdu 1348 凸包模板

http://acm.hdu.edu.cn/showproblem.php?pid=1348

造城墙问题，求出凸包加上一圈圆的周长即可

凸包模板题

#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <cstring>
#include <string>
#include <queue>
#include <map>
#include <iostream>
#include <algorithm>
using namespace std;
#define RD(x) scanf("%d",&x)
#define RD2(x,y) scanf("%d%d",&x,&y)
#define RD3(x,y,z) scanf("%d%d%d",&x,&y,&z)
#define clr0(x) memset(x,0,sizeof(x))
#define eps 1e-9
const double pi = acos(-1.0);
typedef long long LL;
const int modo = 1e9 + 7;
const int maxn = 1e4 + 5;
struct point{
    int x,y;
}a[maxn];
int b[maxn];
bool cmp(point a,point b)
{
    return a.x < b.x || (a.x == b.x && a.y < b.y);
}
double dis(point a,point b)
{
    return sqrt(double((a.x-b.x)*(a.x-b.x)) + double((a.y - b.y)*(a.y - b.y)));
}
int cj(point a,point b,point c)
{
    return (a.x - c.x) * (b.y - c.y) - (a.y - c.y) *(b.x - c.x);
}
int m;
void graham(int n)
{
    sort(a,a+n,cmp);
    b[0] = 0,b[1] = 1,b[2] = 2;
    int k = 1;
    for(int i = 2;i < n;++i){
        while(k && cj(a[i],a[b[k]],a[b[k-1]]) >= 0)
            --k;
        b[++k] = i;
    }
    m = k;
    b[++k] = n - 2;
    for(int i = n - 3;i >= 0;--i){
        while(k != m && cj(a[i],a[b[k]],a[b[k-1]]) >= 0)
            --k;
        b[++k] = i;
    }
    m = k;
}
int main() {
    int n,_;double f;
    RD(_);
    while(_--){
        RD(n);
        scanf("%lf",&f);
        for(int i = 0;i < n;++i){
            RD2(a[i].x,a[i].y);
        }
        graham(n);
        double ans = 0;
        for(int i = 0;i < m;++i)
            ans += dis(a[b[i]],a[b[i+1]]);
        ans += dis(a[b[m]],a[b[0]]);
        ans += pi * 2 *f;
        printf("%.0lf
",ans);
        if(_>0)
            puts("");
    }
    return 0;
}