题解 | #平行四边形#

#include<bits/stdc++.h>
using namespace std;
//struct stu{
//    double x;
//    double y;
//}kk[5];
int T;
double x[5],y[5];
double w(int i, int j){
    return (x[i]-x[j])/(y[i]-y[j]);
}
bool f(int i, int j) {return x[i]==x[j] && y[i]==y[j];} 
bool g(int a, int b, int c, int d) {return x[d]-x[c]==x[b]-x[a] && y[d]-y[c]==y[b]-y[a];}//平行&&相等 
int main(){
    cin>>T;
    while(T--){
        cin>>x[1]>>y[1]>>x[2]>>y[2]>>x[3]>>y[3]>>x[4]>>y[4];
        if(f(1, 2) || f(1, 3) || f(1, 4) || f(2, 3) || f(2, 4) || f(3, 4)) {
            puts("NO"); 
            continue;
        }
        if(w(1, 2)==w(1, 3) || w(1, 2)==w(1, 4)|| w(1, 3)==w(1, 4) || w(2, 3)== w(2, 4)) {
            puts("NO");
            continue;
        }
        if(g(1, 2, 3, 4) || g(1, 2, 4, 3) || g(1, 3, 2, 4) || g(1, 3, 4, 2) || g(1, 4, 2, 3) || g(1, 4, 3, 2)) puts("YES");
        else puts("NO");
    }
}