poj1584A Round Peg in a Ground Hole

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题意甚是难懂！这是第二遍做这道题了，依旧无法理解题意，搜了下题意。。。

首先需要判断是不是为凸多边形。（从一个顶点走一遍即可，要注意顺逆时针，题目中没有指明）

其次看一下圆是不是能够放入多边形内。（首先判断一下圆心是否在圆内，然后枚举圆心到所有边的距离与半径r进行比较）

 #include <iostream>
 #include<cstdio>
 #include<cstring>
 #include<algorithm>
 #include<stdlib.h>
 #include<vector>
 #include<cmath>
 #include<queue>
 #include<set>
 using namespace std;
 #define N 10000
 #define LL long long
 #define INF 0xfffffff
 const double eps = 1e-;
 const double pi = acos(-1.0);
 const double inf = ~0u>>;
 #define _sign(x) ((x) > eps?1:((x) < -eps ? 2 :0))
 struct Point
 {
     double x,y;
     Point(double x=,double y=):x(x),y(y) {}
 }p[N],ch[N];
 int top;
 struct Circle
 {
     Point c;
     double r;
     //Circle(Point c,double r):c(c),r(r){}
     Point point (double a)
     {
         return Point(c.x+cos(a)*r,c.y+sin(a)*r);
     }
 };
 typedef Point pointt;
 pointt operator + (Point a,Point b)
 {
     return Point(a.x+b.x,a.y+b.y);
 }
 pointt operator - (Point a,Point b)
 {
     return Point(a.x-b.x,a.y-b.y);
 }
 double cross(Point a,Point b)
 {
     return a.x*b.y-a.y*b.x;
 }
 double mul(Point p0,Point p1,Point p2)
 {
     return cross(p1-p0,p2-p0);
 }
 double dis(Point a)
 {
     return sqrt(a.x*a.x+a.y*a.y);
 }
 //精度判正负
 int dcmp(double x)
 {
     if(fabs(x)<eps) return ;
     else return x<?-:;
 }
 int Graham(int n)
 {
     int i,s[] = {,,};
     double t;
     for(i = ; i < n&&s[]|s[]; i ++)
     {
         t = mul(p[(i+)%n],p[(i+)%n],p[i]);
         s[_sign(t)] = ;
     }
     return s[]|s[];
 }
 double distoline(Point p,Point a,Point b)
 {
     Point v1 = b-a,v2 = p-a;
     return fabs(cross(v1,v2)/dis(v1));
 }
 int inside(Point po,int n)
 {
     int i,s[] = {,,};
     double t;
     for(i = ;i < n&&s[]|s[];i ++)
     {
         t = mul(p[(i+)%n],po,p[i]);
         s[_sign(t)] = ;
     }
     return s[]|s[];
 }
 int main()
 {
     int n,i;
     Circle cc;
     while(scanf("%d",&n)!=EOF)
     {
         if(n<) break;
         scanf("%lf%lf%lf",&cc.r,&cc.c.x,&cc.c.y);
         for(i  = ; i < n; i++)
         scanf("%lf%lf",&p[i].x,&p[i].y);
         top = ;
         int m = Graham(n);
         if(!m)
         {
             puts("HOLE IS ILL-FORMED");
             continue;
         }
         int flag = ;
         if(!inside(cc.c,n))
         {
             puts("PEG WILL NOT FIT");
             continue;
         }
         for(i = ; i < n; i ++)
         {
             if(dcmp(distoline(cc.c,p[i],p[i-])-cc.r)<)
             {
                 flag = ;
                 break;
             }
         }
         if(!flag)
         puts("PEG WILL NOT FIT");
         else
         puts("PEG WILL FIT");
     }
     return ;
 }