hdu 1392 凸包周长

直接上模板，不过模板还不够精练，以后再慢慢优化

/*
 * hdu1392/win.cpp
 * Created on: 2011-10-22
 * Author    : ben
 */
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <ctime>
#include <iostream>
#include <algorithm>
#include <queue>
#include <set>
#include <map>
#include <stack>
#include <string>
#include <vector>
#include <deque>
#include <list>
#include <functional>
#include <numeric>
#include <cctype>
using namespace std;
const int MAXN = 110;
const double eps = 1e-8;
#define zero(x) (((x)>0?(x):-(x))<eps)
typedef double typec;
typedef struct {
    typec x;
    typec y;
} MyPoint;
inline double xmult(MyPoint p1, MyPoint p2, MyPoint p0) {
    return (p1.x - p0.x) * (p2.y - p0.y) - (p2.x - p0.x) * (p1.y - p0.y);
}
MyPoint p1, p2;
inline bool graham_less(const MyPoint& a, const MyPoint& b) {
    double ret = xmult(a, b, p1);
    if (zero(ret)) {
        return xmult(a, b, p2) < 0;
    } else {
        return ret < 0;
    }
}
void _graham(int n, MyPoint* p, int& s, MyPoint* ch) {
    int i, k = 0;
    for (p1 = p2 = p[0], i = 1; i < n; p2.x += p[i].x, p2.y += p[i].y, i++) {
        if (p1.y - p[i].y > eps || (zero(p1.y - p[i].y) && p1.x > p[i].x)) {
            p1 = p[k = i];
        }
    }
    p2.x /= n, p2.y /= n;
    p[k] = p[0], p[0] = p1;
    sort(p + 1, p + n, graham_less);
    for (ch[0] = p[0], ch[1] = p[1], ch[2] = p[2], s = i = 3; i < n; ch[s++] =
            p[i++]) {
        for (; s > 2 && xmult(ch[s - 2], p[i], ch[s - 1]) < -eps; s--) {
            ;
        }
    }
}
//构造凸包接口函数,传入原始点集大小n,点集p(p原有顺序被打乱!)
//返回凸包大小,凸包的点在convex中
//参数maxsize为1包含共线点,为0不包含共线点,缺省为1
//参数clockwise为1顺时针构造,为0逆时针构造,缺省为1
//在输入仅有若干共线点时算法不稳定,可能有此类情况请另行处理!
//不能去掉点集中重合的点
int graham(int n, MyPoint* p, MyPoint* convex, int maxsize = 1, int dir = 1) {
    MyPoint* temp = new MyPoint[n];
    int s, i;
    _graham(n, p, s, temp);
    convex[0] = temp[0], n = 1, i = (dir ? 1 : (s - 1));
    for (; dir ? (i < s) : i; i += (dir ? 1 : -1) ) {
    if (maxsize || !zero(xmult(temp[i-1],temp[i],temp[(i+1)%s]))) {
        convex[n++]=temp[i];
    }
}
    delete[] temp;
    return n;
}
inline double mydistance(MyPoint &p1, MyPoint &p2) {
    double deltax = p1.x - p2.x;
    double deltay = p1.y - p2.y;
    return sqrt(deltax * deltax + deltay * deltay);
}
MyPoint points[MAXN], tubao[MAXN];

int main() {
#ifndef ONLINE_JUDGE
    freopen("data.in", "r", stdin);
#endif
    int n, m;
    double ans;
    while (scanf("%d", &n) == 1 && n > 0) {
        for (int i = 0; i < n; i++) {
            scanf("%lf%lf", &points[i].x, &points[i].y);
        }
        ans = 0;
        if (n == 2) {
            ans = mydistance(points[0], points[1]);
        } else {
            m = graham(n, points, tubao);
            for (int i = 0; i < m; i++) {
                ans += mydistance(tubao[i], tubao[(i + 1) % m]);
            }
        }
        printf("%.2f\n", ans);
    }
    return 0;
}