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

 

 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\n", minCover);

78     }

79     return 0;

80 }

代码君