排序PointF数组

Question

Could anyone help me with creating an algoritm, IComparer, or some method that would sort an array or list of PointF elements. Lets say I got following PointF elements in my array:

• [0] { X = 50.0 Y = 0.0}
• [1] { X = 100.0 Y = 100.0}
• [2] { X = 0.0 Y = 100.0}
• [3] { X = 100.0 Y = 0.0}
• [4] { X = 0.0 Y = 0.0}
• [5] { X = 100.0 Y = 50.0}
• [6] { X = 50.0 Y = 100.0}

What I would want to achieve is:

• first are elements with lowest Y and X
• still elements with lowest Y but X would get bigger
• then as the highest possible X at this lowest Y get achieved it would go, all elements with this X , but with bigger and bigger Y
• as the top Y and top X get achieved, it would go from elements with top X and top Y , to elements still with top Y , but with lower and lower X

So this sorted array would look something like this:

• [4] { X = 0.0 Y = 0.0}
• [0] { X = 50.0 Y = 0.0}
• [3] { X = 100.0 Y = 0.0}
• [5] { X = 100.0 Y = 50.0}
• [1] { X = 100.0 Y = 100.0}
• [6] { X = 50.0 Y = 100.0}
• [2] { X = 0.0 Y = 100.0}

Meaning, that at the end, if I were to draw these points using Graphics.DrawPolygon() I would get a closed polygon(in this case a rectangle) with no lines crossing each other.

Thank you for your time

Answer 1

The algorithm you want is the Graham Scan. You can read about it here:

http://en.wikipedia.org/wiki/Graham_scan

juharr's comment is correct; you're not going to be able to do this with IComparable because this is not a comparison sort problem . For a comparison sort to work, you need to be able to compare any two elements for relative size.

An easier-but-slower algorithm is the gift wrapping algorithm:

http://en.wikipedia.org/wiki/Gift_wrapping_algorithm

FYI the shape you are looking for is called the convex hull . That will help you when searching for algorithms.