HackerEarth Perpendicular Lines problem solution

#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define si(x) scanf("%d", &x)
#define sc(x) scanf("%c", &x)
#define sl(x) scanf("%lld", &x)
#define pl(x) printf("%lldn", x)
#define pi(x) printf("%dn", x)
#define gu getchar_unlocked
#define pu putchar_unlocked
#define setbits __builtin_popcountll
#define pb push_back
#define mp make_pair
#define MOD 1000000007
#define speed ios::sync_with_stdio(false)

ll gcd(ll a, ll b){
  if(b == 0){
    return a;
  }
  else{
    return gcd(b, a % b);
  }
}


int main(){
  int t;
  si(t);
  while(t--){
    
    ll x1, x2, x3, x4, y1, y2, y3, y4, m1num, m2num, m1den, m2den;
    sl(x1); sl(y1); sl(x2); sl(y2);
    sl(x3); sl(y3); sl(x4); sl(y4);

    if(x1 == x2 && y1 == y2){          
      printf("INVALIDn");
    }
    else if(x3 == x4 && y3 == y4){
      printf("INVALIDn");
    }
    else{
      m1num = y2 - y1; m1den = x2 - x1;
      m2num = y4 - y3; m2den = x4 - x3;

      if(m1den == 0 && m2den == 0){
        printf("NOn");
      }
      else if(m1den == 0){ 
        if(m2num == 0){
          printf("YESn");
        }
        else{
          printf("NOn");
        }
      }
      else if(m2den == 0){
        if(m1num == 0){
          printf("YESn");
          
        }
        else{
          printf("NOn");
        }
      }
      else{          
        int neg = 0;
        if(m1num < 0){
          neg++;
        }
        if(m2num < 0){
          neg++;
        }
        if(m1den < 0){
          neg++;
        }
        if(m2den < 0){
          neg++;
        }
      
        ll p = gcd(abs(m1num), abs(m1den));
        ll q = gcd(abs(m2num), abs(m2den));
        m1num /= p; m1den /= p;
        m2num /= q; m2den /= q;
      
        if(abs(m1num) == abs(m2den) && abs(m2num) == abs(m1den) && neg % 2 == 1){
          printf("YESn");
        }
        else{
          printf("NOn");
        }
      }
    
    }
  }
}