高速公路（Highway，ACM/ICPC SEERC 2005,UVa1615)

I think:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
struct port
{
    long long x,y,l,r;
};
int cmp(const void *a,const void *b)
{
    struct port *x=(struct port *)a;
    struct port *y=(struct port *)b;
    return x->l - y->l;

}
struct port p[1000000];
int main(void)
{
    long long wayLen,d,i,v,sum;
    long long c,tem;
    while(scanf("%lld%lld%lld",&wayLen,&d,&v)!=EOF)
    {
        sum=1;
        for(i=0; i<v; i++)
        {
            scanf("%lld%lld",&p[i].x,&p[i].y);
            c=sqrt(d*d-p[i].y*p[i].y);
            p[i].r=c+p[i].x;
            p[i].l=p[i].x-c;
        }
        qsort(p,v,sizeof(p[0]),cmp);
        tem=p[0].r;
        for(i=1; i<v; i++)
        {
            if(p[i].l<=tem)
                continue;
            else
            {
                tem=p[i].r;
                ++sum;
            }
        }
        printf("%lld\n",sum);
    }
    return 0;
}