这题又写抽了,目测SPJ没有Discuss里面说的那么坑吧。一遍非规范半平面交,然后求最远点对,用的是类似于旋转卡壳找对踵点的方法。一开始还很脑残地写成最大直径问题了……去……
#include <algorithm> #include <iostream> #include <fstream> #include <sstream> #include <iomanip> #include <map> #include <set> #include <list> #include <stack> #include <queue> #include <deque> #include <vector> #include <string> #include <bitset> #include <memory> #include <complex> #include <numeric> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <math.h> #include <time.h> #include <ctype.h> #include <locale.h> using namespace std; #pragma pack(4) const double eps = 1e-8; const double pi = acos(-1.0); const int inf = 0x7f7f7f7f; #define loop(a,n) \ for(int i=0;n>i;i++) \ cout<<a[i]<<(i!=n-1?' ':'\n') #define loop2(a,n,m) \ for(int i=0;n>i;i++) \ for(int j=0;m>j;j++) \ cout<<a[i][j]<<(j!=m-1?' ':'\n') #define at(a,i) ((a)&(1<<(i))) #define nt(a,i) ((a)^(1<<(i))) #define set1(a,i) ((a)|(1<<(i))) #define set0(a,i) ((a)&(~(1<<(i)))) #define cmp(a,b) (fabs((a)-(b))<eps?0:(((a)-(b))>eps?+1:-1)) #define lmax(a,b) ((a)>(b)?(a):(b)) #define lmin(a,b) ((a)<(b)?(a):(b)) #define fmax(a,b) (cmp(a,b)>0?(a):(b)) #define fmin(a,b) (cmp(a,b)<0?(a):(b)) const int MAXV = 102; typedef struct Point { double o[2]; double & operator [] (int i) { return o[i]; } friend ostream & operator << (ostream & cout,Point argu) { return cout<<"("<<argu[0]<<","<<argu[1]<<")"; } Point(double x=0,double y=0) { o[0]=x; o[1]=y; } Point operator + (Point argu) { return Point(o[0]+argu[0],o[1]+argu[1]); } Point operator - (Point argu) { return Point(o[0]-argu[0],o[1]-argu[1]); } Point operator + (double argu) { return (*this)*(1+argu/length()); } Point operator - (double argu) { return (*this)*(1-argu/length()); } Point operator * (double argu) { return Point(o[0]*argu,o[1]*argu); } Point operator / (double argu) { return Point(o[0]/argu,o[1]/argu); } bool operator < (Point argu) const { if(cmp(o[0],argu[0])!=0) return cmp(o[0],argu[0])<0; else return cmp(o[1],argu[1])<0; } bool operator == (Point argu) const { return cmp(o[0],argu[0])==0&&cmp(o[1],argu[1])==0; } double length(void) { return sqrt(o[0]*o[0]+o[1]*o[1]); } double angle(void) { return fmod(atan2(o[1],o[0])+2*pi,2*pi); } }Vector; double dot(Vector a,Vector b) { return a[0]*b[0]+a[1]*b[1]; } double dot(Point o,Point a,Point b) { return dot(a-o,b-o); } int ward(Point p,Point s,Point e) { return cmp(dot(s,e,p),0); } double cross(Vector a,Vector b) { return a[0]*b[1]-a[1]*b[0]; } double cross(Point o,Point a,Point b) { return cross(a-o,b-o); } int side(Point p,Point s,Point e) { return cmp(cross(s,e,p),0); } double area(Point poly[],int n) { double ans=0; for(int i=1;n>i+1;i++) { ans+=cross(poly[0],poly[i],poly[i+1]); } return abs(ans)/2; } int boundingBox(double x,double a,double b) { return cmp(a,x)*cmp(x,b); } int boundingBox(Point p,Point s,Point e) { if(boundingBox(p[0],s[0],e[0])>0&&boundingBox(p[1],s[1],e[1])>0) return 1; else if(boundingBox(p[0],s[0],e[0])>=0&&boundingBox(p[1],s[1],e[1])>=0) return 0; else return -1; } int locate(Point p,Point s,Point e) { if(p==s||p==e) return 0; return side(p,s,e)==0&&boundingBox(p,s,e)>=0?1:-1; } int locate(Point p,Point poly[],int n) { int cnt[3]={0}; poly[n]=poly[0]; for(int i=0;n>i;i++) { cnt[side(p,poly[i],poly[i+1])+1]=true; if(cnt[1]) return 0; if(cnt[2]&&cnt[0]) return -1; } return 1; } int intersection(Point s1,Point e1,Point s2,Point e2) { if(side(s1,s2,e2)*side(e1,s2,e2)<0&&side(s2,s1,e1)*side(e2,s1,e1)<0) return 1; else { if(locate(s1,s2,e2)>=0) return 0; if(locate(e1,s2,e2)>=0) return 0; if(locate(s2,s1,e1)>=0) return 0; if(locate(e2,s1,e1)>=0) return 0; return -1; } } struct Line { Point s,e; double o[3],angle; double & operator [] (int i) { return o[i]; } friend ostream & operator << (ostream & cout,Line argu) { return cout<<"["<<argu.s<<"->"<<argu.e<<"]"; return cout<<"["<<argu[0]<<","<<argu[1]<<" "<<argu[2]<<"]"; } Line(Point s,Point e) { this->s=s; this->e=e; o[0]=s[1]-e[1]; o[1]=e[0]-s[0]; o[2]=cross(s,e); angle=(e-s).angle(); } Line(double a=0,double b=0,double c=1) { o[0]=a; o[1]=b; o[2]=c; if(cmp(a,0)!=0) { s=Point(-c/a,0); e=s+dir(); } else if(cmp(b,0)!=0) { s=Point(0,-c/b); e=s+dir(); } angle=(e-s).angle(); } Line operator + (double argu) { return Line(s+pen()*argu/pen().length(),e+pen()*argu/pen().length()); } Line operator - (double argu) { return Line(s-pen()*argu/pen().length(),e-pen()*argu/pen().length()); } bool operator < (Line argu) const { if(cmp(angle,argu.angle)!=0) return cmp(angle,argu.angle)<0; else return side(argu.s,s,e)<0; } bool operator == (Line argu) const { return cmp(angle,argu.angle)==0; } Vector dir(void) const { return Vector(o[1],-o[0]); } Vector pen(void) const { return Vector(o[0],+o[1]); } }; int ward(Point p,Line l) { return ward(p,l.s,l.e); } int side(Point p,Line l) { return side(p,l.s,l.e); } #ifndef SPECIAL #define SPECIAL Point solve(double a1,double b1,double c1,double a2,double b2,double c2) { Point A(a1,a2); Point B(b1,b2); Point R(c1,c2); return Point(cross(R,B),cross(A,R))/cross(B,A); } Point meet(Line a,Line b) { return solve(a[0],a[1],a[2], b[0],b[1],b[2]); } Point foot(Point p,Line l) { return solve(l[0],l[1],l[2], l[1],-l[0],l[0]*p[1]-l[1]*p[0]); } Point symmetry(Point p,Line l) { return solve(l[0],l[1],l[0]*p[0]+l[1]*p[1]+2*l[2], l[1],-l[0],l[0]*p[1]-l[1]*p[0]); } #endif // SPECIAL #ifndef DIS #define DIS double dis(Point a,Point b) { return (b-a).length(); } double disPar(Point p,Line l) { return dot(l.s,l.e,p)/dis(l.s,l.e); } double disPen(Point p,Line l) { return cross(l.s,l.e,p)/dis(l.s,l.e); } double dis(Point p,Point s,Point e) { if(ward(p,s,e)*ward(p,e,s)>0) return disPen(p,Line(s,e)); else return fmin(dis(p,s),dis(p,e)); } double dis(Line a,Line b) { if(cmp(a.angle,b.angle)!=0) return 0; else return disPen(a.s,b); } double dis(Line l,Point s,Point e) { if(side(s,l)*side(e,l)<0) return 0; else return fmin(disPen(s,l),disPen(e,l)); } double dis(Point s1,Point e1,Point s2,Point e2) { if(intersection(s1,e1,s2,e2)>=0) return 0; else return fmin(fmin(dis(s1,s2,e2),dis(e1,s2,e2)),fmin(dis(s2,s1,e1),dis(e2,s1,e1))); } #endif // DIS int n; double r,x,y; Line l[MAXV],plane[MAXV]; Point p[MAXV],convex[MAXV]; int HPI(Line l[],int n) { int f=0,r=-1,cnt=0; n=(sort(l,l+n),unique(l,l+n))-l; for(int i=0;n>i;i++) { while(f<r&&side(meet(plane[r-1],plane[r]),l[i])<0) r--; while(f<r&&side(meet(plane[f+1],plane[f]),l[i])<0) f++; plane[++r]=l[i]; } while(f<r&&side(meet(plane[r-1],plane[r]),plane[f])<0) r--; while(f<r&&side(meet(plane[f+1],plane[f]),plane[r])<0) f++; for(int i=f;i<r;i++) convex[cnt++]=meet(plane[i],plane[i+1]); convex[cnt++]=meet(plane[f],plane[r]); return cnt; } Line rotateCliper(Point poly[],int n) { int f=1; Point s=poly[0],e=poly[0]; p[n]=p[0]; for(int i=0;n>i;i++) { while(cmp(dis(poly[i],poly[f+1]),dis(poly[i],poly[f]))>0) f=(f+1)%n; if(cmp(dis(poly[i],poly[f]),dis(s,e))>=0) { s=poly[i]; e=poly[f]; } } return Line(s,e); } int main() { #ifndef ONLINE_JUDGE freopen("Feng Shui.txt","r",stdin); #else #endif while(scanf("%d %lf",&n,&r)!=EOF) { for(int i=0;n>i;i++) { scanf("%lf %lf",&x,&y); p[i]=Point(x,y); } for(int i=0;n>i;i++) { l[i]=Line(p[(i+1)%n],p[i])+r; } Line ans=rotateCliper(convex,HPI(l,n)); printf("%.6f %.6f %.6f %.6f\n",ans.s[0],ans.s[1],ans.e[0],ans.e[1]); } return 0; }