Poj1328--Radar Installation(区间选点)

 1 #include <cmath>
 2 #include <cstdio>
 3 #include <algorithm>
 4 using namespace std;
 5 
 6 struct island
 7 {
 8     double l, r; 
 9 } num[1010];
10 
11 bool cmp(island l, island r)
12 {
13     if(l.l == r.l)
14         return l.r < r.r;
15     return l.l < r.l; 
16 }
17 
18 int main()
19 {
20     double r, x, y;    int i, m, t=1;
21     while(~scanf("%d %lf", &m, &r))
22     {
23         int flag = 0;
24         if(m == 0 && r == 0)
25             break;
26         for(i=0; i<m; i++)
27         {
28             scanf("%lf %lf", &x, &y);
29             if(y > r)
30             {flag = 1; continue; }
31             num[i].l = x - sqrt(r*r - y*y);   //转化为区间问题； 
32             num[i].r = x + sqrt(r*r - y*y);
33         }
34         if(flag)
35         {
36             printf("Case %d: -1\n",t++); 
37             continue;
38         }
39         sort(num, num+m, cmp);
40         double temp = num[0].r; int total = 1;
41         for(i=1; i<m; i++)        
42         {
43             if(num[i].l > temp){
44                 total++;
45                 temp = num[i].r;
46             }
47                 
48             if(num[i].l <= temp)
49             {
50                 if(num[i].r < temp)
51                     temp = num[i].r;
52             }
53         }
54         printf("Case %d: %d\n", t++, total); 
55     }
56     return 0;
57 }