poj 2187 Beauty Contest

http://poj.org/problem?id=2187

 1 #include<cstdio>

 2 #include<cstring>

 3 #include<cstdlib>

 4 #include<algorithm>

 5 using namespace std;

 6 

 7 const int maxn=50000;

 8 struct point

 9 {

10     int x,y;

11     bool operator < (const point &a)const

12     {

13         return (x<a.x)||(x==a.x&&y<a.y);

14     }

15 };

16 

17 point p[maxn],ch[maxn];

18 

19 int sqr(int x)

20 {

21     return x*x;

22 }

23 

24 int det(point a,point b,point c)

25 {

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

27 }

28 

29 int dis(point a,point b)

30 {

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

32 }

33 

34 int convex_hull(point *p,int n,point *ch)

35 {

36     sort(p,p+n);

37     int m=0;

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

39     {

40         while(m>1&&det(ch[m-2],ch[m-1],p[i])<=0) m--;

41         ch[m++]=p[i];

42     }

43     int k=m;

44     for(int i=n-2; i>=0; i--)

45     {

46         while(m>k&&det(ch[m-2],ch[m-1],p[i])<=0) m--;

47         ch[m++]=p[i];

48     }

49     if(n>1) m--;

50     return m;

51 }

52 

53 int dia_rotating_calipers(int n)

54 {

55     int dia=0,q=1;

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

57     {

58         while(det(ch[i],ch[i+1],ch[q+1])>det(ch[i],ch[i+1],ch[q]))

59         {

60             q=(q+1)%n;

61         }

62         dia=max(dia,max(dis(ch[i],ch[q]),dis(ch[i+1],ch[q+1])));

63     }

64     return dia;

65 }

66 

67 int main()

68 {

69     int n,cn;

70     scanf("%d",&n);

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

72     {

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

74     }

75     cn=convex_hull(p,n,ch);

76     printf("%d\n",dia_rotating_calipers(cn));

77     return 0;

78 }

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