C# Point in polygon

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I’ve checked codes here and all have problems.

The best method is:

    /// <summary>
    /// Determines if the given point is inside the polygon
    /// </summary>
    /// <param name="polygon">the vertices of polygon</param>
    /// <param name="testPoint">the given point</param>
    /// <returns>true if the point is inside the polygon; otherwise, false</returns>
    public static bool IsPointInPolygon4(PointF[] polygon, PointF testPoint)
    {
        bool result = false;
        int j = polygon.Count() - 1;
        for (int i = 0; i < polygon.Count(); i++)
        {
            if (polygon[i].Y < testPoint.Y && polygon[j].Y >= testPoint.Y || polygon[j].Y < testPoint.Y && polygon[i].Y >= testPoint.Y)
            {
                if (polygon[i].X + (testPoint.Y - polygon[i].Y) / (polygon[j].Y - polygon[i].Y) * (polygon[j].X - polygon[i].X) < testPoint.X)
                {
                    result = !result;
                }
            }
            j = i;
        }
        return result;
    }

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