POJ 2007 极角排序

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题目扯了那么多，又是算斜率，又是不同象限的，最后就是一个极角排序
注意，这里的极角排序是一般grahm-scan算法的逆序即可

#include <iostream>#include <cstdio>#include <cmath>#include <cstring>#include <algorithm>const int maxn=55;const double eps=1e-8;using namespace std;int sgn(double x){    if(fabs(x)<eps)        return 0;    if(x>0)        return 1;    if(x<0)        return -1;}struct point{    double x,y;    //double slope=0;    point(){}    point(double _x,double _y){        x=_x;        y=_y;    }};typedef point vector;vector operator - (vector a,vector b){    return point(a.x-b.x,a.y-b.y);}double operator * (vector a,vector b){    return a.x*b.x+a.y*b.y;}double operator ^ (vector a,vector b){    return a.x*b.y-a.y*b.x;}bool operator < (vector a,vector b){    if(a.x==b.x &&a.y<b.y ||a.x<b.x)        return true;    return false;}double dis(point a,point b){    return hypot(a.x-b.x,a.y-b.y);}struct convex{    int n;    point p[maxn];};point p[maxn];bool cmp(point a,point b){    int d=sgn((a-p[0])^(b-p[0]));    if(d<0 || d==0 && sgn(dis(a,p[0])-dis(b,p[0]))<0 )//d<0 逆序       return true;    return false;}int main(){    //freopen("input.txt","r",stdin);    int i=0;    while(~scanf("%lf%lf",&p[i].x,&p[i].y))        i++;    sort(p,p+i,cmp);    printf("(%d,%d)\n",int(p[0].x),int(p[0].y));    for(int j=i-1;j>0;j--)        printf("(%d,%d)\n",int(p[j].x),int(p[j].y));}

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