HDU 1912

坑，直接把公路看成X轴来做，然后，排序扫描一下，你懂的。

#include <iostream>
#include <algorithm>
#include <cstdio>
#include <cmath>
using namespace std;

const int MAXN=10100;

struct Village{
	double l,r;
};
Village p[MAXN];

bool cmp(Village A, Village B){
	if(A.l<B.l)return true;
	else if(A.l==B.l){
		if(A.r<B.r)return true;
	}
	return false;
}

int main(){
	int n,L,D; double x,y;
	while(scanf("%d%d%d",&L,&D,&n)!=EOF){
		for(int i=0;i<n;i++){
			scanf("%lf%lf",&x,&y);
			double d=sqrt(D*D-y*y);
			p[i].l=x-d; p[i].r=x+d;
		}
		int counted=1;
		sort(p,p+n,cmp);
		double s=p[0].r;
		for(int i=1;i<n;i++){
			if(p[i].l<=s)
			continue;
			else{
				s=p[i].r;
				counted++;
			}
		}
		printf("%d\n",counted);
	}
	return 0;
}