poj 1328 Radar Installation(贪心+快排)

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <cmath>
 4 #include <algorithm>
 5 #include <cstring>
 6 #include <cstdlib>
 7 using namespace std;
 8 #define MAX 1005
 9 struct sea
10 {
11     double left;
12     double right;
13 } a[1005];
14 bool operator < (sea A,sea B)
15 {
16     return A.left<B.left;
17 }
18 int main()
19 {
20     int n,k=1;
21     double d;
22     while(cin>>n>>d&&(n||d))
23     {
24         bool flag=false;
25         for(int i=0; i<n; i++)
26         {
27             double x,y;
28             cin>>x>>y;
29             if(fabs(y)>d)
30                 flag=true;
31             else
32             {  //计算区间
33                 a[i].left=x*1.0-sqrt(d*d-y*y);
34                 a[i].right=x*1.0+sqrt(d*d-y*y);
35             }
36         }
37         printf("Case %d: ",k++);
38         if(flag)
39             printf("-1\n");
40         else
41         {
42             int ans=1; //雷达初始化
43             sort(a,a+n); //  排序
44             double s=a[0].right;
45             for(int i=1; i<n; i++)
46             {
47                 if(a[i].left>s)
48                 {
49                     ans++;    //雷达加一
50                     s=a[i].right; // 更新右端点
51                 }
52                 else if(a[i].right<s)
53                     s=a[i].right;
54             }
55             printf("%d\n",ans);
56         }
57     }
58     return 0;
59 }