HDU1392

来源：互联网发布：淘宝上办签证被骗了编辑：程序博客网时间：2024/06/05 20:28

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=1392

凸包模板题，但是特别注意只有两个点的情况，MD两个点只能输出两点间的距离，可是题目上明明说的是surround围绕啊，MDZZ。

#include <iostream>#include <cstdio>#include <cmath>#include <algorithm>using namespace std;const double eps = 1e-10;struct Point{    double x, y;    Point() {}    Point(double x_, double y_): x(x_), y(y_) {}    bool operator < (const Point& a) const    {        if (x == a.x)            return y < a.y;        return x < a.x;    }    bool operator == (const Point& a) const    {        if (x == a.x && y == a.y)            return true;        return false;    }};typedef Point Vector;Point P[110], convex[110];Vector operator - (Point A, Point B){    return Vector(A.x-B.x, A.y-B.y);}double Length(Point A, Point B){    return sqrt((A.x-B.x)*(A.x-B.x) + (A.y-B.y)*(A.y-B.y));}double Cross(Vector A, Vector B) //A × B{    return A.x*B.y - A.y*B.x;}int ConvexHull(Point *p, int n, Point *ch){    int m = 0;    sort(p, p+n);    n = unique(p, p+n) - p;    for (int i=0; i<n; i++)    {        while (m > 1 && Cross(ch[m-1]-ch[m-2], p[i]-ch[m-2]) <= 0) m--;        ch[m++] = p[i];    }    int k = m;    for (int i=n-2; i>=0; i--)    {        while (m > k && Cross(ch[m-1]-ch[m-2], p[i]-ch[m-2]) <= 0) m--;        ch[m++] = p[i];    }    return m;}int main(){    int n;    while (scanf("%d",&n))    {        if (!n)            break;        for (int i=0; i<n; i++)            scanf("%lf%lf",&P[i].x, &P[i].y);        if (n == 1)        {            printf("%.2lf\n",0);            continue;        }        else if (n == 2)        {            printf("%.2lf\n",Length(P[0],P[1]));            continue;        }        int cnt = ConvexHull(P, n, convex);        double ans = 0;        for (int i=1; i<cnt; i++)            ans += Length(convex[i-1],convex[i]);        printf("%.2lf\n",ans);    }    return 0;}

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