和 Uva 10020几乎是一样的，不过这里要把圆形区域转化为能够覆盖的长条形区域(一个小小的勾股定理)
学习一下别人的代码，练习使用STL的vector容器
这里有个小技巧，用一个微小量EPS来弥补浮点运算中的误差
1 //#define LOCAL 2 #include <vector> 3 #include <cstdio> 4 #include <cmath> 5 #include <algorithm> 6 #include <functional> 7 using namespace std; 8 9 const int MAXN = 10240; 10 const double EPS = 1e-11; 11 12 struct Range 13 { 14 double a, b; 15 inline bool operator< (const Range& rhs) const 16 { 17 return a < rhs.a || (a == rhs.a && b < rhs.b); 18 } 19 }; 20 21 int main(void) 22 { 23 #ifdef LOCAL 24 freopen("10382in.txt", "r", stdin); 25 #endif 26 27 int n, l, w; 28 double lenth, width; 29 vector<Range> ranges; 30 ranges.reserve(MAXN);//reserve()函数提前设定容量大小，避免多次容量扩充操作导致效率低下 31 32 while(scanf("%d%d%d", &n, &l, &w) == 3) 33 { 34 lenth = (double)l; 35 width = w / 2.0; 36 ranges.clear(); 37 38 for(int i = 0; i < n; ++i) 39 { 40 int position, radius; 41 double xw; 42 Range range; 43 44 scanf("%d%d", &position, &radius); 45 if(radius * 2 <= w) continue; 46 xw = sqrt((double)radius * radius - width * width); 47 48 range.a = position - xw; 49 if(range.a > lenth + EPS) continue; 50 else if(range.a - EPS < 0.0) range.a = 0.0; 51 range.b = position + xw; 52 ranges.push_back(range); 53 } 54 55 sort(ranges.begin(), ranges.end()); 56 57 int minCover = 0; 58 double start = 0.0, end = 0.0; 59 for(vector<Range>::iterator pr = ranges.begin(); pr != ranges.end(); ) 60 { 61 start = end; 62 if(pr->a > start + EPS) 63 { 64 minCover = -1; 65 break; 66 } 67 ++minCover; 68 while(pr != ranges.end() && pr->a <= start) 69 { 70 if(pr->b > end + EPS) end = pr->b; 71 ++pr; 72 } 73 if(end > lenth + EPS) 74 break; 75 } 76 if(end + EPS < lenth) minCover = -1; 77 printf("%d ", minCover); 78 } 79 return 0; 80 }