uva 10382 - Watering Grass（区域覆盖问题）

#include <string.h>
#include <math.h>
#include <algorithm>
using namespace std;
int n,f;;
double l, w;
double s, t;
struct qujian
{
    double start;
    double end;
} ;
qujian a[10005];
int cmp(qujian a,qujian b)
{
    return a.end > b.end;
}
int main()
{
    while (~scanf("%d%lf%lf", &n, &l, &w))
 
 while (scanf("%d%lf%lf", &n, &l, &w)==3)

//在此，要加==3或者为~scanf(),不然会超时
    {
        double start=0;
        f= 0;
        for (int i = 0; i < n; i ++)
        {
            scanf("%lf%lf", &s, &t);
            a[i].start = v - sqrt(r * r - w * w / 4); //开平方必须用double型，这里的式子是勾股定理
            a[i].end = v + sqrt(r * r - w * w / 4);
        }
        sort(a,a+ n, cmp);
        while (start<l)
        {
            int i;
            for (i = 0; i < n; i ++)
            {
                if (a[i].start <=start&& a[i].end>start)
                {
                    start=a[i].end;
                    f++;
                    break;
                }
            }
            if(i==n)
                break;
        }
        if (start<l) printf("-1\n");
        else printf("%d\n",f);
    }
    return 0;
}