POJ 1228 Grandpa's Estate

第一次做凸包，2Y，^ ^

#include<iostream>#include<string>#include<cstring>#include<cmath>#include<cstdio>using namespace std;int n,pos;struct point{    int x,y;}p[1010];const int inf=0x7fffffff;int mult(point a,point b,point c){    if((a.x-b.x)*(a.y-c.y)<(a.y-b.y)*(a.x-c.x))        return 1;    if((a.x-b.x)*(a.y-c.y)==(a.y-b.y)*(a.x-c.x))        return -1;    return 0;}bool dist(point a,point b,point c){    return (a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y)>(a.x-c.x)*(a.x-c.x)+(a.y-c.y)*(a.y-c.y);}bool jarvis(point pp){    int i;    point tmp=p[pos];    bool flag=false;    for(i=0;i<n;i++)       // if(!vis[i])        {            int judge=mult(pp,tmp,p[i]);            if(judge==1)            {                flag=false;                tmp=p[i];            }            else if(judge==-1)            {                flag=true;                if(dist(pp,p[i],tmp))                    tmp=p[i];            }        }    if(!flag)        return false;    if(p[pos].x==tmp.x&&p[pos].y==tmp.y)        return true;    jarvis(tmp);}int main(){    int t,i,minx,miny;   // freopen("sample.txt","r",stdin);    cin>>t;    while(t--)    {        minx=miny=inf;        cin>>n;        for(i=0;i<n;i++)        {            cin>>p[i].x>>p[i].y;            if(p[i].x<minx)            {                pos=i;                minx=p[i].x;                miny=p[i].y;            }            else if(p[i].x==minx&&miny>p[i].y)            {                pos=i;                miny=p[i].y;            }        }        if(n>=6&&jarvis(p[pos]))            cout<<"YES"<<endl;        else            cout<<"NO"<<endl;    }return 0;}