POJ2526+简单几何

题意：给定的这些点是否有一个对称中心。

PS：我写得有点啰嗦。。

就是把小的x和大的x进行匹配。

#include<stdio.h>
#include<algorithm>
#include<math.h>
using namespace std;

const double eps = 1e-8;
const int maxn = 10005;

struct Point{
    double x,y;
};
Point pnt1[ maxn ],pnt2[ maxn ];
Point cc;

int cmp1( Point a,Point b ){
    return a.x<b.x;
}

int cmp2( Point a,Point b ){
    return a.y<b.y;
}

int cmp3( Point a,Point b ){
    return a.x>b.x;
}

bool NotOnePoint( Point a,Point b ){
    if( fabs(a.x-b.x)<=eps&&fabs(a.y-b.y)<=eps ) return false;
    else return true;
}

bool OK( Point a,Point b ){
    if( fabs((a.x+b.x)-(2.0*cc.x))<=eps && fabs((a.y+b.y)-(2.0*cc.y))<=eps ) return true;
    else return false;
}

bool Notcc( Point a ){
    if( fabs(a.x-cc.x)<=eps&&fabs(a.y-cc.y)<=eps ) return true;
    else return false;
}

int main(){
    int n;
    int T;
    //freopen("in.txt","r",stdin);
    scanf("%d",&T);
    while( T-- ){
        scanf("%d",&n);
        for( int i=1;i<=n;i++ ){
            scanf("%lf%lf",&pnt1[i].x,&pnt1[i].y);
            pnt2[ i ] = pnt1[ i ];
        }
        if( n==2 ){
            puts("yes");
            continue;
        }
        sort( pnt1+1,pnt1+1+n,cmp1 );
        cc.x = (pnt1[1].x+pnt1[n].x)/2.0;
        sort( pnt2+1,pnt2+1+n,cmp2 );
        cc.y = (pnt2[1].y+pnt2[n].y)/2.0;
        sort( pnt2+1,pnt2+1+n,cmp3 );

        int cnt = 0;
        if( n%2==1 ){
            for( int i=1;i<=n;i++ ){
                if( pnt1[i].x==cc.x&&pnt1[i].y==cc.y ){
                    cnt++;
                }
            }
        }
        if( (n-cnt)%2==1 ){
            puts("no");
            continue;
        }
        if( n==cnt ){
            puts("yes");
            continue;
        }
        //printf("cc:x = %lf,y = %lf
",cc.x,cc.y);
        /*
        for( int i=1;i<=n;i++ ){
            printf("x = %lf 
",pnt1[i].x);
        }
        for( int i=1;i<=n;i++ ){
            printf("x = %lf 
",pnt2[i].x);
        }
        */
        int tt = 0;
        int N = n - cnt;//N%2=0
        for( int i=1;i<=(n/2)&&tt<(N/2);i++ ){
            tt++;
            //printf(" i =%d ",i);
            //printf("pnt1:x = %lf y = %lf
",pnt1[i].x,pnt1[i].y);
            bool find = false;
            for( int j=1;j<=(n/2);j++ ){
                //printf(" j = %d 
",j);
                //printf("pnt2:x = %lf y = %lf
",pnt2[j].x,pnt2[j].y);
                if( (pnt1[i].x+pnt2[j].x)<2.0*cc.x ) break;
                if( /*Notcc(pnt1[i])==true&&*/NotOnePoint(pnt1[i],pnt2[j])==true&&OK(pnt1[i],pnt2[j])==true ){
                    find = true;
                    cnt += 2;
                    break;
                }
            }
            //if( find==true ) printf("true
");
            //else printf("false
");
            if( find==false ) break;
        }
        if( cnt==n ){
            puts("yes");
            continue;
        }
        puts("no");
    }
    return 0;
}