Difference between revisions of "Newbie Code Critique"
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==[[Graham Scan Implementation]]== |
==[[Graham Scan Implementation]]== |
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| − | Descriptions of the problem can be found in [http://book.realworldhaskell.org/read/defining-types-streamlining-functions.html Real World Haskell, Chapter 3] |
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| − | <haskell> |
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| − | --Graham Scan exercise |
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| − | |||
| − | --Direction type |
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| − | data Direction = LeftTurn |
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| − | | RightTurn |
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| − | | Straight |
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| − | deriving (Show, Eq) |
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| − | |||
| − | --Point type |
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| − | data Point = Point (Double, Double) |
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| − | deriving (Show) |
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| − | |||
| − | --some points |
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| − | p0 = Point (2.1,2.0) |
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| − | p1 = Point (4.2,2.0) |
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| − | p2 = Point (0.5,2.5) |
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| − | p3 = Point (3.2,3.5) |
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| − | p4 = Point (1.2,4.0) |
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| − | p5 = Point (0.7,4.7) |
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| − | p6 = Point (1.0,1.0) |
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| − | p7 = Point (3.0,5.2) |
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| − | p8 = Point (4.0,4.0) |
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| − | p9 = Point (3.5,1.5) |
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| − | pA = Point (0.5,1.0) |
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| − | points = [p0,p1,p2,p3,p4,p5,p6,p7,p8,p9,pA] |
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| − | |||
| − | --Get direction of single set of line segments |
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| − | dir :: Point -> Point -> Point -> Direction |
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| − | dir (Point (ax, ay)) (Point (bx, by)) (Point (cx, cy)) = case sign of |
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| − | EQ -> Straight |
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| − | GT -> LeftTurn |
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| − | LT -> RightTurn |
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| − | where sign = compare ((bx - ax) * (cy - ay) - (by - ay) * (cx - ax)) 0 |
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| − | |||
| − | --Get a list of Directions from a list of Points |
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| − | dirlist :: [Point] -> [Direction] |
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| − | dirlist (x:y:z:xs) = dir x y z : dirlist (y:z:xs) |
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| − | dirlist _ = [] |
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| − | |||
| − | --Compare Y axes |
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| − | sortByY :: [Point] -> [Point] |
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| − | sortByY xs = sortBy lowestY xs |
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| − | where lowestY (Point(x1,y1)) (Point (x2,y2)) = if y1 == y2 |
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| − | then compare x1 x2 |
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| − | else compare y1 y2 |
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| − | --get COT of line defined by two points and the x-axis |
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| − | pointAngle :: Point -> Point -> Double |
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| − | pointAngle (Point (x1, y1)) (Point (x2, y2)) = (x2 - x1) / (y2 - y1) |
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| − | |||
| − | --compare based on point angle |
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| − | pointOrdering :: Point -> Point -> Ordering |
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| − | pointOrdering a b = compare (pointAngle a b) 0.0 |
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| − | |||
| − | --Sort by angle |
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| − | sortByAngle :: [Point] -> [Point] |
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| − | sortByAngle ps = bottomLeft : sortBy (compareAngles bottomLeft) (tail (sortedPs)) |
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| − | where sortedPs = sortByY ps |
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| − | bottomLeft = head (sortedPs) |
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| − | |||
| − | |||
| − | |||
| − | --Compare angles |
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| − | compareAngles :: Point -> Point -> Point -> Ordering |
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| − | compareAngles base a b = compare (pointAngle base b) (pointAngle base a) |
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| − | |||
| − | --Graham Scan |
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| − | gscan :: [Point] -> [Point] |
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| − | gscan ps = scan (sortByAngle ps) |
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| − | where scan (x:y:z:xs) = if dir x y z == RightTurn |
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| − | then x: scan (z:xs) |
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| − | else x: scan (y:z:xs) |
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| − | scan (x:y:[]) = (x:y:[]) |
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| − | scan _ = [] |
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| − | </haskell> |
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Revision as of 15:30, 26 September 2009
This page is a place for new users to post pieces of code that they want analyzed.