Uva 10382 (区间覆盖) Watering Grass

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

 //#define LOCAL
 #include <vector>
 #include <cstdio>
 #include <cmath>
 #include <algorithm>
 #include <functional>
 using namespace std;

 const int MAXN = ;
 const double EPS = 1e-;

 struct Range
 {
     double a, b;
     inline bool operator< (const Range& rhs) const
     {
         return a < rhs.a || (a == rhs.a && b < rhs.b);
     }
 };

 int main(void)
 {
     #ifdef LOCAL
         freopen("10382in.txt", "r", stdin);
     #endif

     int n, l, w;
     double lenth, width;
     vector<Range> ranges;
     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

     while(scanf("%d%d%d", &n, &l, &w) == )
     {
         lenth = (double)l;
         width = w / 2.0;
         ranges.clear();

         for(int i = ; i < n; ++i)
         {
             int position, radius;
             double xw;
             Range range;

             scanf("%d%d", &position, &radius);
             if(radius *  <= w)    continue;
             xw = sqrt((double)radius * radius - width * width);

             range.a = position - xw;
             if(range.a > lenth + EPS)    continue;
             else if(range.a - EPS < 0.0)    range.a = 0.0;
             range.b = position + xw;
             ranges.push_back(range);
         }

         sort(ranges.begin(), ranges.end());

         int minCover = ;
         double start = 0.0, end = 0.0;
         for(vector<Range>::iterator pr = ranges.begin(); pr != ranges.end(); )
         {
             start = end;
             if(pr->a > start + EPS)
             {
                 minCover = -;
                 break;
             }
             ++minCover;
             while(pr != ranges.end() && pr->a <= start)
             {
                 if(pr->b > end + EPS)    end = pr->b;
                 ++pr;
             }
             if(end > lenth + EPS)
                 break;
         }
         if(end + EPS < lenth)    minCover = -;
         printf("%d\n", minCover);
     }
     return ;
 }

代码君