uva 1615 （区间选点）

#include <cstdio>
#include <algorithm>
#include <cmath>
#define eps 1e-7
using namespace std;
const int maxn = 10000+10;
struct village {
double o,l;
bool operator < (const village& b) const {
return l<b.l || fabs(l-b.l)<=eps && o > b.o;
}
}a[maxn];
int main()
{
int L, D;
double u, v, t;
int n;
while(scanf("%d%d%d",&L,&D,&n) != EOF) {
for(int i(0); i < n; i++) {
scanf("%lf%lf",&u,&v);
t = sqrt(D*D - v*v);
a[i].o = max(u-t,0.0); a[i].l = min(u+t,(double)L);
}
sort(a,a+n);
//for(int o=0;o<n;o++) printf("(%lf,%lf) ",a[o].o,a[o].l);
int cnt(1); double pos = a[0].l;
for(int i(0); i < n; i++) {
if(pos<a[i].o) {pos=a[i].l;cnt++;}
}
printf("%d\n",cnt);
}
}