POJ 2007 Scrambled Polygon（简单极角排序）

水题，根本不用凸包，就是一简单的极角排序。

叉乘<0，逆时针。

#include <iostream>#include <cstdio>#include <cstring>#include <string>#include <algorithm>using namespace std;const int maxn=55;struct point{    double x,y;} p[maxn];double cross(point c1,point b1,point a2){    return (b1.x-c1.x)*(a2.y-c1.y)-(b1.y-c1.y)*(a2.x-c1.x);}bool cmp(point a,point b){    point c;    c.x=0;c.y=0;    return cross(c,b,a)<0;}int main(){    int n=0;    while(scanf("%lf %lf",&p[n].x,&p[n].y)!=EOF)        n++;    sort(p+1,p+n, cmp);    for(int i =0; i<n; i++)        cout<<"("<<p[i].x<<","<<p[i].y<<")"<<endl;    return 0;}