Radar Installation -poj 1328

 1 #include <iostream>
 2 #include<math.h>
 3 #include <algorithm>
 4 #include <stdlib.h>
 5 using namespace std;
 6 struct point
 7 {
 8     double left, right;
 9 }points[1000], temp;
10 
11 bool operator < (point a, point b)
12 {
13     return a.left < b.left;
14 }
15 int main() {
16     int num = 0;
17     double rad = 0;
18     cin >> num >> rad;
19     int casenum=1;
20     while (num || rad) {
21 
22 
23         int rnum=1;
24         int wrong = 0;
25 
26         for (int i = 0; i < num; i++) {
27             double x=0;
28             double y=0;
29             cin >> x >> y;
30 
31             if (y > rad) {
32                 //岛屿纵坐标大于雷达半径
33                 wrong = 1;
34             }else{
35                 //以岛屿为圆心，做圆，与x轴的交点
36                 points[i].left=x-sqrt((rad*rad-y*y)*1.0);
37                 points[i].right=x+sqrt((rad*rad-y*y)*1.0);
38 
39             }
40         }
41         if (wrong) {
42             //雷达不能覆盖
43             cout<<"Case "<<casenum++<<": "<<-1<<endl;
44         } else {
45             //按照岛屿画圆与x轴的左交点排序
46             sort(points, points + num);
47              temp=points[0];
48             for(int i=1;i<num;i++){
49                 //
50                 if(points[i].left>temp.right)//temp.right为公共区间的右端点，若下一个区间的左端点大于temp.right则该区间与以上的公共区间没有公共部分
51                 {
52                     rnum++;//雷达个数加1
53                     temp=points[i];//更新公共区间右端点
54                 }else if(points[i].right<temp.right){
55                      temp=points[i];//更新公共区间右端点
56                 }
57                 }
58 
59             cout<<"Case "<<casenum++<<": "<<rnum<<endl;
60         }
61 
62         cin >> num >> rad;
63     }
64     return 0;
65 }