一本通1424： 区间覆盖

给一些区间，挑出最少的区间覆盖 【0，L】

 

  贪心：从0往后，每次挑出R 点最大的

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#include <iostream> #include <algorithm> #include <cstring> #include <cmath> using namespace std ;  const int N=1e5;  int n;     struct T{     double x,y;  };  T a[N];  int cmp(T x,T y){ return x.x<y.x; }     void solve(double end){     double cur=0;     int i=1, ans=0;           while(cur<end){         ans++;         double t=cur;         for(;a[i].x<=t&&i<=n;i++)             cur=max(cur,a[i].y);                   if(cur==t&&t<end){             cout<<-1<<endl; return ;         }     }     cout<<ans<<endl;  }  int main(){     int i,tmp; double x,L,h,r;     int cas; cin>>cas;           while(cas--){         cin>>tmp>>L>>h;         n=0;         for(i=1;i<=tmp;i++){             cin>>x>>r;             if(r<h/2) continue;             n++;             a[n].x=x-sqrt(r*r-h*h/4);             a[n].y=x+sqrt(r*r-h*h/4);          }         sort(a+1,a+1+n,cmp);         solve(L);     }  }