poj 2007 Scrambled Polygon 极角排序

 1 /**

 2 极角排序输出，，，

 3 主要atan2（y，x） 容易失精度，，用

 4 bool cmp(point a,point b){

 5     if(cross(a-tmp,b-tmp)>0)

 6         return 1;

 7     if(cross(a-tmp,b-tmp)==0)

 8         return length(a-tmp)<length(b-tmp);

 9     return 0;

10 }

11 **/

12 #include <iostream>

13 #include <algorithm>

14 #include <cmath>

15 using namespace std;

16

17 struct point {

18     double x,y;

19     point (double x=0,double y=0):x(x),y(y){}

20 };

21 point p[100];

22 point tmp;

23 typedef point Vector;

24 Vector operator - (point a,point b){

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

26 }

27 double angle(Vector v){

28     return atan2(v.y,v.x);

29 }

30 double length(Vector v){

31     return sqrt(v.x*v.x+v.y*v.y);

32 }

33

34 double cross(Vector a,Vector b){

35     return a.x*b.y-a.y*b.x;

36 }

37 bool cmp(point a,point b){

38     if(cross(a-tmp,b-tmp)>0)

39         return 1;

40     if(cross(a-tmp,b-tmp)==0)

41         return length(a-tmp)<length(b-tmp);

42     return 0;

43 }

44

45 int main()

46 {

47     int cnt =0;

48     double x1,y1;

49     cin>>tmp.x>>tmp.y;

50     while(cin>>x1>>y1){

51         p[cnt].x = x1;

52         p[cnt].y = y1;

53         cnt++;

54     }

55     sort(p,p+cnt,cmp);

56     cout<<"("<<tmp.x<<","<<tmp.y<<")"<<endl;

57     for(int i=0;i<cnt;i++)

58         cout<<"("<<p[i].x<<","<<p[i].y<<")"<<endl;

59     return 0;

60 }

poj 2007 Scrambled Polygon 极角排序