YbtOJ 824「计算几何初探」圆与连线

#include<bits/stdc++.h>
#define Tp template<typename Ty>
#define Ts template<typename Ty,typename... Ar>
#define W while
#define I inline
#define RI register int
#define LL long long
#define Cn const
#define CI Cn int&
#define gc getchar
#define D isdigit(c=gc())
#define pc(c) putchar((c))
#define min(x,y) ((x)<(y)?(x):(y))
#define max(x,y) ((x)>(y)?(x):(y))
using namespace std;
namespace Debug{
    Tp I void _debug(Cn char* f,Ty t){cerr<<f<<'='<<t<<endl;}
    Ts I void _debug(Cn char* f,Ty x,Ar... y){W(*f!=',') cerr<<*f++;cerr<<'='<<x<<",";_debug(f+1,y...);}
    Tp ostream& operator<<(ostream& os,Cn vector<Ty>& V){os<<"[";for(Cn auto& vv:V) os<<vv<<",";os<<"]";return os;}
    #define gdb(...) _debug(#__VA_ARGS__,__VA_ARGS__)
}using namespace Debug;
namespace FastIO{
    Tp I void read(Ty& x){char c;int f=1;x=0;W(!D) f=c^'-'?1:-1;W(x=(x<<3)+(x<<1)+(c&15),D);x*=f;}
    Ts I void read(Ty& x,Ar&... y){read(x),read(y...);}
    Tp I void write(Ty x){x<0&&(pc('-'),x=-x,0),x<10?(pc(x+'0'),0):(write(x/10),pc(x%10+'0'),0);}
    Tp I void writeln(Cn Ty& x){write(x),pc('\n');}
}using namespace FastIO;
Cn int N=2e3+10;Cn double pi=acos(-1);
int n,r,Ans;
#define PA pair<double,double>
#define MP make_pair
#define fi first
#define se second
PA a[N];double f[N];
int main(){
    freopen("circle.in","r",stdin),freopen("circle.out","w",stdout);
    RI i,j,x,y,top;double ang,cir;for(read(n,r),i=1;i<=n;i++) read(x,y),ang=atan2(y,x),cir=acos(1.0*r/sqrt(x*x+y*y)),(a[i].fi=ang-cir)<-pi&&(a[i].fi+=2*pi),(a[i].se=ang+cir)>pi&&(a[i].se-=2*pi),a[i].fi>a[i].se&&(swap(a[i].fi,a[i].se),0);
    for(sort(a+1,a+n+1),i=1;i<=n;i++){
        f[top=0]=a[i].se;for(j=i+1;j<=n;j++) if(a[j].fi>a[i].se) break ;else if(a[j].se>a[i].se) f[top]<=a[j].se?f[++top]=a[j].se:*lower_bound(f+1,f+top+1,a[j].se)=a[j].se;Ans=max(Ans,top+1);
    }return writeln(Ans),0;
}