POJ 1328 Radar Installation

事实上，一个点被一个圆覆盖可以转化成区间问题。

#include<cstdio>
#include<cstring>
#include<cmath>
#include<queue>
#include<algorithm>
using namespace std;

const int maxn=1000+10;
struct X
{
    double x,y;
    double L,R;
} s[maxn];
double d;
int n;
bool fail;

bool cmp(const X&a,const X&b)
{
    if(a.L==b.L) return a.R<b.R;
    return a.L<b.L;
}

int main()
{
    int T=1;

    while(~scanf("%d%lf",&n,&d))
    {
        if(n==0&&d==0) break;
        fail=0;
        for(int i=1; i<=n; i++)
            scanf("%lf%lf",&s[i].x,&s[i].y);
        for(int i=1; i<=n; i++)
        {
            if(s[i].y>d) fail=1;
            s[i].L=s[i].x-sqrt(d*d-s[i].y*s[i].y);
            s[i].R=s[i].x+sqrt(d*d-s[i].y*s[i].y);
        }
        sort(s+1,s+1+n,cmp);
        int ans=0;
        double st=-123456789,en=-123456789;
        for(int i=1; i<=n; i++)
        {
            if(s[i].L>=st&&s[i].L<=en)
            {
                st=max(st,s[i].L);
                en=min(en,s[i].R);
            }
            else
            {
                ans++;
                st=s[i].L;
                en=s[i].R;
            }
        }
        printf("Case %d: ",T++);
        if(fail) printf("-1\n");
        else printf("%d\n",ans);
    }
    return 0;
}