Algorithm to calculate number of intersecting discs

Question

Given an array A of N integers we draw N discs in a 2D plane, such that i-th disc has center in (0,i) and a radius

Answer 1

This got 100/100 in c#

class CodilityDemo3
{

    public static int GetIntersections(int[] A)
    {
        if (A == null)
        {
            return 0;
        }

        int size = A.Length;

        if (size <= 1)
        {
            return 0;
        }

        List lines = new List();

        for (int i = 0; i < size; i++)
        {
            if (A[i] >= 0)
            {
                lines.Add(new Line(i - A[i], i + A[i]));
            }
        }

        lines.Sort(Line.CompareLines);
        size = lines.Count;
        int intersects = 0;

        for (int i = 0; i < size; i++)
        {
            Line ln1 = lines[i];
            for (int j = i + 1; j < size; j++)
            {
                Line ln2 = lines[j];
                if (ln2.YStart <= ln1.YEnd)
                {
                    intersects += 1;
                    if (intersects > 10000000)
                    {
                        return -1;
                    }
                }
                else
                {
                    break;
                }
            }
        }

        return intersects;
    }

}

public class Line
{
    public Line(double ystart, double yend)
    {
        YStart = ystart;
        YEnd = yend;
    }
    public double YStart { get; set; }
    public double YEnd { get; set; }

    public static int CompareLines(Line line1, Line line2)
    {
        return (line1.YStart.CompareTo(line2.YStart));

    }
}

}