83 lines
2.1 KiB
C++
83 lines
2.1 KiB
C++
#include<stdio.h>
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#include<string.h>
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#include<algorithm>
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#include<math.h>
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using namespace std;
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#define PR 1e-8
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#define N 50015
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struct TPoint
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{
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double x,y;
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TPoint(){}
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TPoint(double _x,double _y):x(_x),y(_y){}
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TPoint operator-(const TPoint p) {return TPoint(x-p.x,y-p.y);}
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}ply[N];
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int n;
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double MAX(double a,double b) {return a>b?a:b;}
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double dist(TPoint a,TPoint b)
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{
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TPoint c(b-a);
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return sqrt(c.x*c.x+c.y*c.y);
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}
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double cross(TPoint a,TPoint b,TPoint c)
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{
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TPoint s(b-a),t(c-a);
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return s.x*t.y-s.y*t.x;
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}
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int dblcmp(double a)
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{
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if(fabs(a)<PR) return 0;
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return a>0?1:-1;
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}
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bool cmpx(TPoint a,TPoint b)
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{
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if(fabs(a.x-b.x)<PR) return a.y<b.y;
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return a.x<b.x;
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}
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bool cmp(TPoint a,TPoint b)
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{
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int d1=dblcmp(cross(ply[0],a,b));
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return d1>0||(d1==0&&dist(ply[0],a)<dist(ply[0],b));
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}
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double diss(TPoint a,TPoint b)
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{
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return dist(a,b)*dist(a,b);
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}
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int main()
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{
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while(~scanf("%d",&n))
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{
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int i,top=2,j,p,q,r;
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for(i=0;i<n;i++)
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scanf("%lf%lf",&ply[i].x,&ply[i].y);
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sort(ply,ply+n,cmpx);
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sort(ply+1,ply+n,cmp);
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for(i=2;i<n;i++)
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{
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while(top>1&&(dblcmp(cross(ply[top-2],ply[i],ply[top-1])))>=0) top--;
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ply[top++]=ply[i];
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}
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double max1=-1e20,tmp;
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n=top; ply[n]=ply[0]; ply[n+1]=ply[1]; ply[n+2]=ply[2];
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p=0; q=1; r=2;
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while(1)
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{
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int pp=p,qq=q,rr=r;
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while(cross(ply[p],ply[q],ply[r+1])-(tmp=cross(ply[p],ply[q],ply[r]))>PR)
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r=(r+1)%n;
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max1=MAX(max1,fabs(tmp)*0.5);
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while(cross(ply[p],ply[q+1],ply[r])-(tmp=cross(ply[p],ply[q],ply[r]))>PR)
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q=(q+1)%n;
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max1=MAX(max1,fabs(tmp)*0.5);
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while(cross(ply[p+1],ply[q],ply[r])-(tmp=cross(ply[p],ply[q],ply[r]))>PR)
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p=(p+1)%n;
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max1=MAX(max1,fabs(tmp)*0.5);
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if(pp==p&&qq==q&&rr==r) r=(r+1)%n;
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if(r==0) break;
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}
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if(n<3) max1=0;
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printf("%.2lf\n",max1);
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}
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return 0;
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}
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