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| #include<cstdio>
#include<cmath>
#include<vector>
#include<algorithm>
using namespace std;
double L,D;
struct node{
double l,r;
node(const double &x,const double &y){
double R=sqrt(D*D-y*y);
this->l=max(x-R,0.0),this->r=min(x+R,L);
return;
}
bool operator < (const node &x) const {
return r==x.r?l>x.l:r<x.r;
}
};
vector<node> vil;
int main(){
while(~scanf("%lf%lf",&L,&D)){
vil.clear();
int n,cnt=1;
scanf("%d",&n);
for(int i=0;i<n;++i){
double x,y;
scanf("%lf%lf",&x,&y);
vil.push_back(node(x,y));
}
sort(vil.begin(),vil.end());
double pos=vil[0].r;
for(int i=0;i<(int)vil.size();++i){
if(pos<=vil[i].r&&pos>=vil[i].l) continue;
pos=vil[i].r,++cnt;
}
printf("%d\n",cnt);
}
return 0;
}
|