poj1696Space Ant（逆时针螺旋形）

链接

贪心做法，没次找最外面的点，也就是相对前面那条线偏转角度最小的点，除第一个点需要找到最下面的点即Y坐标最小，其余的每次进行极角排序。

 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 55

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 int o[55];

18 struct Point

19 {

20     int x,y;

21     Point(double x=0,double y=0):x(x),y(y) {}

22     int id;

23 }p[N];

24 int cc;

25 typedef Point pointt;

26 pointt operator + (Point a,Point b)

27 {

28     return Point(a.x+b.x,a.y+b.y);

29 }

30 pointt operator - (Point a,Point b)

31 {

32     return Point(a.x-b.x,a.y-b.y);

33 }

34 double dis(Point a)

35 {

36     return sqrt(1.0*a.x*a.x+a.y*a.y);

37 }

38 int cross(Point a,Point b)

39 {

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

41 }

42 int mul(Point p0,Point p1,Point p2)

43 {

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

45 }

46 

47 bool cmp(Point a,Point b)

48 {

49     if(mul(p[cc],a,b)==0)

50         return dis(a-p[cc])<dis(b-p[1]);

51     else

52         return mul(p[cc],a,b)>0;

53 }

54 int main()

55 {

56     int t,i,n;

57     cin>>t;

58     while(t--)

59     {

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

61         for(i = 1; i <= n ;i++)

62         {

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

64         }

65         int tmp = 1;

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

67         if(p[tmp].y>p[i].y)

68         {

69             tmp = i;

70         }

71         swap(p[1],p[tmp]);

72         int g = 0;

73         o[++g] = p[1].id;

74         cc = 1;

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

76         {

77             sort(p+i,p+n+1,cmp);

78             o[++g] = p[i].id;

79             cc = i;

80         }

81         printf("%d",g);

82         for(i = 1 ;i <= g;  i++)

83         printf(" %d",o[i]);

84         puts("");

85     }

86     return 0;

87 }

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