poj1696 Space Ant

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题目链接：http://poj.org/problem?id=1696
题意：给你n个点的坐标，并给出每个点的序号，让你找一条，不向右拐的最长的路径
解析：每次都找到一个基准点做极角排序，下一次则选则相对于之前那一个点最小极角的点，再接着进行极角排序，这样生成的路径就是所求的

#include <cstdio>#include <cstring>#include <algorithm>#include <cmath>#include <iostream>#include <vector>#include <queue>#include <set>using namespace std;const int maxn = 1000+100;struct point{    int id;    double x,y;    point() {}    point(double _x,double _y)    {        x = _x;        y = _y;    }    bool operator < (const point &b)const    {        if(y==b.y)            return x<b.x;        return y<b.y;    }}a[maxn];int cnt = 0;double x_mul(point p0,point p1,point p2){    return (p1.x-p0.x)*(p2.y-p0.y)-(p2.x-p0.x)*(p1.y-p0.y);}double dis(point a,point b){    return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));}int cmp(point p1,point p2){    if(x_mul(a[cnt],p1,p2)==0)        return dis(a[cnt],p1)<dis(a[cnt],p2);    return x_mul(a[cnt],p1,p2)>0;}int main(){    int t;    cin>>t;    while(t--)    {        int n;        scanf("%d",&n);        for(int i=0;i<n;i++)            scanf("%d %lf %lf",&a[i].id,&a[i].x,&a[i].y);        sort(a,a+n);        cnt = 0;        for(int i=1;i<n;i++)        {            sort(a+i,a+n,cmp);            cnt++;        }        printf("%d",n);        for(int i=0;i<n;i++)            printf(" %d",a[i].id);        puts("");    }    return 0;}

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