POJ 1328 Radar Installation

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

const int MAXN = 1000+5;
int n, d;
int x[MAXN], y[MAXN];
pair<double, double> p[MAXN];

void solve()
{
    double offset;
    for(int i = 0; i < n; ++i){
        if(d < y[i]){
            printf("-1\n");
            return;
        }
        offset = sqrt(d*d-y[i]*y[i]);
        p[i].first = x[i]-offset;
        p[i].second = x[i]+offset;
    }
    sort(p, p+n);
    int res = 1;
    double l = p[0].first, r = p[0].second;
    for(int i = 1; i < n; ++i){
        if(p[i].first > r){
            ++res;
            l = p[i].first;
            r = p[i].second;
        }
        else{
            l = max(l, p[i].first);
            r = min(r, p[i].second);
        }
    }
    printf("%d\n", res);
}

int main()
{
    int cn = 0;
    while(scanf("%d%d", &n, &d), n){
        for(int i = 0; i < n; ++i)
            scanf("%d%d", &x[i], &y[i]);
        printf("Case %d: ", ++cn);
        solve();
    }
    return 0;
}