poj 3277 Mountains

http://poj.org/problem?id=3227

 1 #include <cstdio>

 2 #include <cstring>

 3 #include <cmath>

 4 #include <algorithm>

 5 #define maxn 2000

 6 using namespace std;

 7 

 8 int n,h;

 9 const double eps=1e-8;

10 int cmp(double x)

11 {

12     if(fabs(x)<eps) return 0;

13     if(x>0) return 1;

14     return -1;

15 }

16 struct point

17 {

18     double x,y;

19     point() {}

20     point(double a,double b):x(a),y(b) {}

21 } p[maxn];

22 

23 double sqr(double x)

24 {

25     return x*x;

26 }

27 

28 double dis(point a,point b)

29 {

30     return (sqrt(sqr(a.x-b.x)+sqr(a.y-b.y)));

31 }

32 

33 double det(point a,point b,point c,point d)

34 {

35     return (b.x-a.x)*(d.y-c.y)-(b.y-a.y)*(d.x-c.x);

36 }

37 

38 bool segem(point a,point b,point c,point d,point &e)

39 {

40     double s1=det(a,b,a,c);

41     double s2=det(a,b,a,d);

42     e.x=(c.x*s2-d.x*s1)/(s2-s1);

43     e.y=(c.y*s2-d.y*s1)/(s2-s1);

44     return true;

45 }

46 

47 double kk(point a,point b)

48 {

49     return (b.y-a.y)/(b.x-a.x);

50 }

51 int main()

52 {

53     while(scanf("%d%d",&n,&h)!=EOF)

54     {

55         if(n==0&&h==0) break;

56         for(int i=0; i<n; i++)

57         {

58             scanf("%lf%lf",&p[i].x,&p[i].y);

59         }

60         point res;

61         res.x=0;

62         res.y=h;

63         double sum=0;

64         sum+=dis(p[0],p[1]);

65         point key;

66         key=p[1];

67         for(int i=2; i<n; i++)

68         {

69             double k3=kk(res,p[i]);

70             double k1=kk(p[i],p[i-1]);

71             double k2=kk(res,key);

72             if(k3-k2>eps)

73             {

74                 if(k1-k2>=0)

75                 {

76                     point e;

77                     segem(res,key,p[i-1],p[i],e);

78                     sum+=dis(e,p[i]);

79                     key=p[i];

80                 }

81             }

82         }

83         printf("%.2lf\n",sum);

84     }

85     return 0;

86 }

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