Problem:
Parallel/Orthogonal

For given two lines s1 and s2, print "2" if they are parallel, "1" if they are orthogonal, or "0" otherwise.

s1 crosses points p0 and p1, and
s2 crosses points p2 and p3.

Input

The entire input looks like:

q (the number of queries)
1st query
2nd query
...
qth query

Each query consists of integer coordinates of the points p0, p1, p2, p3 in the following format:

xp0 yp0 xp1 yp1 xp2 yp2 xp3 yp3

Output

For each query, print "2", "1" or "0".

Constraints

1 ≤ q ≤ 1000

-10000 ≤ xpi, ypi ≤ 10000

p0 ≠ p1 and
p2 ≠ p3.

Sample Input 1

3
0 0 3 0 0 2 3 2
0 0 3 0 1 1 1 4
0 0 3 0 1 1 2 2

Sample Output 1

2
1
0

Solution in C# (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Diagnostics;
using Aoj.CGL.Lib;
  
namespace Aoj.CGL.Chapter2A
{
    class Program
    {
        public static void Solve()
        {
            int n = int.Parse(Console.ReadLine());
   
            for (int i = 0; i < n; i++)
            {
                int[] input = Array.ConvertAll(Console.ReadLine().Split(' '), int.Parse);
  
                var seg1 = new Segment(input[0],input[1],input[2],input[3]);
                var seg2 = new Segment(input[4],input[5],input[6],input[7]);
  
                int answer = 0;
                if (Segment.IsOrthogonal(seg1, seg2))
                    answer = 1;
                else if (Segment.IsParallel(seg1, seg2))
                    answer = 2;
  
                Console.WriteLine(answer);
            }
        }
  
        public static void Main()
        {
            // Console.SetIn(new System.IO.StreamReader("ComputationalGeometry/Input/02_Segment_Line_A_01.txt"));
            // var sw = new Stopwatch();
            // sw.Start();
  
            Solve();
  
            // Console.WriteLine("{0}ms", sw.ElapsedMilliseconds);
        }
    }
}
  
namespace Aoj.CGL.Lib
{
    using Line = Segment;

    using Polygon = List<Point>;

    public struct Point
    {
        private double _x;
        private double _y;

        public double X { get { return _x;} }
        public double Y { get { return _y;} }

        public Point(double x, double y)
        {
            _x = x;
            _y = y;
        }

        public static Point operator +(Point p1, Point p2)
        {
            return new Point(p1.X + p2.X, p1.Y + p2.Y);
        }

        public static Point operator -(Point p1, Point p2)
        {
            return new Point(p1.X - p2.X, p1.Y - p2.Y);
        }

        public static Point operator *(Point p, double k)
        {
            return new Point(p.X * k, p.Y * k);
        }

        public static explicit operator Vector(Point p)
        {
            return new Vector(p.X, p.Y);
        }

        public static bool IsOrthogonal(Point a1, Point a2, Point b1, Point b2)
        {
            return Vector.IsOrthogonal((Vector)(a1 - a2), (Vector)(b1 - b2));
        }

        public static bool IsParallel(Point a1, Point a2, Point b1, Point b2)
        {
            return Vector.IsParallel((Vector)(a1 - a2), (Vector)(b1 - b2));
        }
    }

    public struct Segment
    {
        private Point _p1;
        private Point _p2;

        public Point P1 { get{ return _p1; } }
        public Point P2 { get{ return _p2; } }

        public Segment(Point p1, Point p2)
        {
            _p1 = p1;
            _p2 = p2;
        }

        public Segment(double x1, double y1, double x2, double y2)
        {
            _p1 = new Point(x1, y1);
            _p2 = new Point(x2, y2);
        }
        public static bool IsOrthogonal(Segment s1, Segment s2)
        {
            return Vector.IsOrthogonal((Vector)(s1.P1 - s1.P2), (Vector)(s2.P1 - s2.P2));
        }

        public static bool IsParallel(Segment s1, Segment s2)
        {
            return Vector.IsParallel((Vector)(s1.P1 - s1.P2), (Vector)(s2.P1 - s2.P2));
        }
    }

    public struct Circle
    {
        private Point _p;
        private double _r;

        public Point P { get { return _p; } }
        public double R { get { return _r; } }

        public Circle(Point p, double r)
        {
            _p = p;
            _r = r;
        }
    }

    public struct Vector
    {
        private double _x;
        private double _y;

        public double X { get { return _x;} }
        public double Y { get { return _y;} }

        public Vector(double x, double y)
        {
            _x = x;
            _y = y;
        }

        public double Norm()
        {
            return X * X + Y * Y;
        }

        public double Abs()
        {
            return Math.Sqrt(Norm());
        }

        public static Vector operator +(Vector v1, Vector v2)
        {
            return new Vector(v1.X + v2.X, v1.Y + v2.Y);
        }

        public static Vector operator -(Vector v1, Vector v2)
        {
            return new Vector(v1.X - v2.X, v1.Y - v2.Y);
        }

        public static Vector operator *(Vector v, double k)
        {
            return new Vector(v.X * k, v.Y * k);
        }

        public static double Dot(Vector v1, Vector v2)
        {
            return v1.X * v2.X + v1.Y * v2.Y;
        }

        public static double Cross(Vector v1, Vector v2)
        {
            return v1.X * v2.Y - v1.Y * v2.X;
        }

        public static bool IsOrthogonal(Vector v1, Vector v2)
        {
            return Dot(v1, v2) == 0.0;
        }

        public static bool IsParallel(Vector v1, Vector v2)
        {
            return Cross(v1, v2) == 0.0;
        }
    }
}