mirror of
https://github.com/Kiritow/OJ-Problems-Source.git
synced 2024-03-22 13:11:29 +08:00
89 lines
2.5 KiB
C++
89 lines
2.5 KiB
C++
#include<iostream>
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#include<cstdio>
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#include<algorithm>
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#include<cmath>
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#define eps 1e-10
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#define N 50005
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#define zero(a) (fabs(a)<eps)
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using namespace std;
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struct Point {
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double x,y;
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Point(){}
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Point(double tx,double ty){x=tx;y=ty;}
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}p[N],q[N];
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int n,m;
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struct Segment{
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Point s,e;
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double angle;
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void get_angle(){angle=atan2(e.y-s.y,e.x-s.x);}
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}seg[N];
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double xmul(Point p0,Point p1,Point p2){
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return (p1.x-p0.x)*(p2.y-p0.y)-(p2.x-p0.x)*(p1.y-p0.y);
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}
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double Get_Area(Point pt[],int n){
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double area=0;
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for(int i=1;i<n-1;i++)
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area+=xmul(pt[0],pt[i],pt[i+1]);
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return fabs(area)/2;
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}
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Point Get_Intersect(Segment s1,Segment s2){
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double u=xmul(s1.s,s1.e,s2.s),v=xmul(s1.e,s1.s,s2.e);
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Point t;
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t.x=(s2.s.x*v+s2.e.x*u)/(u+v);t.y=(s2.s.y*v+s2.e.y*u)/(u+v);
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return t;
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}
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void HalfPlaneIntersect(Segment seg[],int n){
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int idx;
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for(int i=0;i<n;i++)
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if(seg[i].angle+eps<seg[(i+1)%n].angle&&seg[i].angle+eps<seg[(i-1+n)%n].angle){
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idx=i;
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break;
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}
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Segment deq[N];
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deq[0]=seg[idx];deq[1]=seg[(idx+1)%n];
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int head=0,tail=1;
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idx=(idx+2)%n;
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for(int i=2;i<n;i++,idx=(idx+1)%n){
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while(head<tail&&xmul(seg[idx].s,seg[idx].e,Get_Intersect(deq[tail],deq[tail-1]))<-eps) tail--;
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while(head<tail&&xmul(seg[idx].s,seg[idx].e,Get_Intersect(deq[head],deq[head+1]))<-eps) head++;
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deq[++tail]=seg[idx];
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}
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while(head<tail&&xmul(deq[head].s,deq[head].e,Get_Intersect(deq[tail],deq[tail-1]))<-eps) tail--;
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while(head<tail&&xmul(deq[tail].s,deq[tail].e,Get_Intersect(deq[head],deq[head+1]))<-eps) head++;
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m=0;
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if(tail==head) return;
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for(int i=head;i<tail;i++){
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q[m++]=Get_Intersect(deq[i],deq[i+1]);
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}
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if(tail>head+1)
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q[m++]=Get_Intersect(deq[head],deq[tail]);
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}
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int slove(int mid){
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if(n-mid<=2) return 1;
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for(int i=0;i<n;i++){
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seg[i].s=p[i];
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seg[i].e=p[(i+mid+1)%n];
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seg[i].get_angle();
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}
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HalfPlaneIntersect(seg,n);
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return zero(Get_Area(q,m));
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}
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int main(){
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int t;
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scanf("%d",&t);
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while(t--){
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scanf("%d",&n);
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for(int i=0;i<n;i++)
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scanf("%lf%lf",&p[i].x,&p[i].y);
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for(int i=1;i<=n/2;i++) swap(p[i],p[n-i]);
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int ans,low=0,high=n,mid;
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while(low<=high){
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mid=(low+high)/2;
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if(slove(mid)){ans=mid;high=mid-1;}
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else low=mid+1;
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}
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printf("%d\n",ans);
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}
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return 0;
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}
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