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。

#include <iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<stdlib.h>
#include<vector>
#include<cmath>
#include<queue>
#include<set>
using namespace std;
#define N 55
#define LL long long
#define INF 0xfffffff
const double eps = 1e-8;
const double pi = acos(-1.0);
const double inf = ~0u>>2;
int o[55];
struct Point
{
    int x,y;
    Point(double x=0,double y=0):x(x),y(y) {}
    int id;
}p[N];
int cc;
typedef Point pointt;
pointt operator + (Point a,Point b)
{
    return Point(a.x+b.x,a.y+b.y);
}
pointt operator - (Point a,Point b)
{
    return Point(a.x-b.x,a.y-b.y);
}
double dis(Point a)
{
    return sqrt(1.0*a.x*a.x+a.y*a.y);
}
int cross(Point a,Point b)
{
    return a.x*b.y-a.y*b.x;
}
int mul(Point p0,Point p1,Point p2)
{
    return cross(p1-p0,p2-p0);
}

bool cmp(Point a,Point b)
{
    if(mul(p[cc],a,b)==0)
        return dis(a-p[cc])<dis(b-p[1]);
    else
        return mul(p[cc],a,b)>0;
}
int main()
{
    int t,i,n;
    cin>>t;
    while(t--)
    {
        scanf("%d",&n);
        for(i = 1; i <= n ;i++)
        {
            scanf("%d%d%d",&p[i].id,&p[i].x,&p[i].y);
        }
        int tmp = 1;
        for(i = 2; i <= n; i++)
        if(p[tmp].y>p[i].y)
        {
            tmp = i;
        }
        swap(p[1],p[tmp]);
        int g = 0;
        o[++g] = p[1].id;
        cc = 1;
        for(i = 2 ;i <= n; i++)
        {
            sort(p+i,p+n+1,cmp);
            o[++g] = p[i].id;
            cc = i;
        }
        printf("%d",g);
        for(i = 1 ;i <= g;  i++)
        printf(" %d",o[i]);
        puts("");
    }
    return 0;
}