uva 1421
稍微有点新意的二分
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
#include<cstdio> #include<cstring> #include<algorithm> #include<cmath> #include<queue> #include<vector> #include<iostream> #define eps 0.000001 #define maxn 5005 using namespace std; int n; double w; struct node { double x,y,d; bool operator<(const node &t)const { return d<t.d; } } no[maxn]; int get(double x) { double ll=atan2(no[0].d,no[0].y-x),rr=atan2(no[0].d,no[0].x-x); for(int i=1;i<n;i++) { double l=atan2(no[i].d,no[i].y-x); double r=atan2(no[i].d,no[i].x-x); // printf("%lf %lf++\n",l,r); if(l-rr>eps)return 1; if(r-ll<-eps)return -1; ll=max(ll,l); rr=min(rr,r); } return 0; } bool solve() { double l=0.0,r=w; while(r-l>eps) { double mid=(r+l)/2.0; int k=get(mid); if(k==0)return 1; else if(k==1)l=mid; else r=mid; } return 0; } int main() { int t; scanf("%d",&t); while(t--) { scanf("%lf",&w); scanf("%d",&n); for(int i=0; i<n; i++) { scanf("%lf%lf%lf",&no[i].d,&no[i].x,&no[i].y); } sort(no,no+n); if(solve())puts("YES"); else puts("NO"); } return 0; }