Operation Love

C. Operation Love

先判断给定点是顺时针还是逆时针，然后再判断长度为6的边是在长度为9的边的左边还是右边即可

// Created by CAD
#include <bits/stdc++.h>
using namespace std;
bool judge(vector<double> x,vector<double> y,int n){
    if(n < 3) return 0.0>0;
    double s = y[0] * (x[n - 1] - x[1]);
    x.resize(n+1),y.resize(n+1);
    y[n] = y[0],x[n]=x[0];
    for(int i = 1; i < n; ++ i)
        s += y[i] * (x[i - 1] - x[i + 1]);
    return s * 0.5>0;
}
double dis(double x1,double y1,double x2,double y2){
    return (x2-x1)*(x2-x1)+(y2-y1)*(y2-y1);
}
int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n=20;
    int t;cin>>t;
    while(t--){
        vector<double> x(20),y(20);
        for(int i=0;i<n;++i)
            cin>>x[i]>>y[i];
        if(!judge(x,y,n))
            reverse(x.begin(),x.end()),reverse(y.begin(),y.end());
        bool f1=0,f2=0,ans=0;
        double eps=1;
        for(int i=0;i<n;++i){
            double a=dis(x[i],y[i],x[(i+1)%n],y[(i+1)%n]);
            double b=dis(x[(i+1)%n],y[(i+1)%n],x[(i+2)%n],y[(i+2)%n]);
            if(abs(a-36)<=eps&&abs(b-81)<=eps)
                ans=1;
        }
        if(ans) cout<<"right"<<endl;
        else cout<<"left"<<endl;
    }
    return 0;
}