POJ2007+几何+极角排序

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 1 /*

 2 几何+凸包逆序输出+极角排序

 3 */

 4 #include<stdio.h>

 5 #include<string.h>

 6 #include<stdlib.h>

 7 #include<math.h>

 8 #include<algorithm>

 9 using namespace std;

10 const int maxn = 55;

11 const double eps = 1e-8;

12 struct Point{

13     double x,y;

14 };

15 Point point[ maxn ];

16 

17 double xmult( Point sp,Point ep,Point op ){

18     return ( sp.x-op.x )*( ep.y-op.y )-( sp.y-op.y )*( ep.x-op.x );

19 }

20 

21 int sig( double d ){

22     if( d>eps ) return 1;

23     if( d<-eps ) return -1;

24     return 0;

25 }

26 

27 double dist( Point a,Point b ){

28     double sum = ( a.x-b.x )*( a.x-b.x )+( a.y-b.y )*( a.y-b.y );

29     return sqrt( sum );

30 }

31 

32 int cmp(  Point a, Point b ){

33     return sig( xmult(a,b,point[0]) )>0;

34 }

35 

36 int main(){

37     int n = 0;

38     while( scanf("%lf%lf",&point[ n ].x,&point[ n ].y )!=EOF )

39         n++;

40     sort( point+1,point+n,cmp );

41     for( int i=0;i<n;i++ ){

42         printf("(%.0lf,%.0lf)\n",point[ i ].x,point[ i ].y);

43     }

44     return 0;

45 }