poj2187Beauty Contest(凸包直径）

链接

利用旋转卡壳

参考博客http://www.cppblog.com/staryjy/archive/2010/09/25/101412.html

 1 #include <iostream>

 2 #include<cstdio>

 3 #include<cstring>

 4 #include<algorithm>

 5 #include<stdlib.h>

 6 #include<vector>

 7 #include<cmath>

 8 #include<queue>

 9 #include<set>

10 using namespace std;

11 #define N 50010

12 #define LL long long

13 #define INF 0xfffffff

14 const double eps = 1e-8;

15 const double pi = acos(-1.0);

16 const double inf = ~0u>>2;

17 struct point

18 {

19     int x,y;

20     point(int x=0,int y = 0):x(x),y(y){}

21 }p[N],ch[N];

22 typedef point pointt;

23 pointt operator - (point a,point b)

24 {

25     return point(a.x-b.x,a.y-b.y);

26 }

27 int dcmp(double x)

28 {

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

30     return x<0?-1:1;

31 }

32 double cross(point a,point b)

33 {

34     return 1.0*a.x*b.y-a.y*b.x;

35 }

36 double mul(point p0,point p1,point p2)

37 {

38     return cross(p1-p0,p2-p0);

39 }

40 int dis(point a)

41 {

42     return a.x*a.x+a.y*a.y;

43 }

44 bool cmp(point a,point b)

45 {

46     if(dcmp(mul(p[0],a,b))==0) return dis(a-p[0])<dis(b-p[0]);

47     return dcmp(mul(p[0],a,b))>0;

48 }

49 int graham(int n)

50 {

51     int i,k=0,top;

52     point tmp;

53     for(i = 0;  i< n; i++)

54     {

55         if(p[i].y<p[k].y||(p[i].y==p[k].y&&p[i].x<p[k].x))

56             k = i;

57     }

58     if(k!=0)

59         swap(p[0],p[k]);

60     sort(p+1,p+n,cmp);

61     ch[0] = p[0];

62     ch[1] = p[1];

63     top = 1;

64     for(i = 2; i < n; i++)

65     {

66         while(top>0&&dcmp(mul(ch[top-1],ch[top],p[i]))<=0)

67             top--;

68         ch[++top] = p[i];

69     }

70     return top;

71 }

72 int rotating_calipers(int n)

73 {

74     int q = 1;

75     int ans = 0;

76     ch[n] = ch[0];

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

78     {

79         while(mul(ch[i+1],ch[q+1],ch[i])>mul(ch[i+1],ch[q],ch[i]))

80         q = (q+1)%n;

81         ans = max(ans,max(dis(ch[i]-ch[q]),dis(ch[i+1]-ch[q+1])));

82     }

83     return ans;

84 }

85 int main()

86 {

87     int n,i;

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

89     {

90         for(i = 0; i < n;i++)

91         scanf("%d%d",&p[i].x,&p[i].y);

92         int top = graham(n);

93         int ans = rotating_calipers(top+1);

94         printf("%d\n",ans);

95     }

96     return 0;

97 }

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