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russel-norvig-ai-problems
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Changed to qualified imports

master
Abhinav Sarkar 2012-01-10 01:40:18 +05:30
parent 3108bc9aad
commit 04431eb8e6
1 changed files with 11 additions and 10 deletions
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21
chapter4/SlidingPuzzle.hs
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@ -2,7 +2,8 @@
-- using A* algorithm
import Data.Ix
import Data.Array
import qualified Data.Array as A
import Data.Array (Array, array, (//), (!))
import Data.List
import Data.List.Split
import Data.Maybe
@ -92,7 +93,7 @@ data Puzzle a = Puzzle { blank :: a, pzState :: Array Point a } deriving (Eq, Or
-- Get puzzle size
puzzleSize :: Puzzle a -> Int
puzzleSize = fst . snd . bounds . pzState
puzzleSize = fst . snd . A.bounds . pzState
-- Create a puzzle give the blank, the puzzle size and the puzzle state as a list,
-- left to right, top to bottom.
@ -109,19 +110,19 @@ showPuzzleState :: Show a => Puzzle a -> String
showPuzzleState pz =
('\n' :) . concat . intersperse "\n"
. map (concat . intersperse " ") . splitEvery len
. map show . elems . pzState $ pz
. map show . A.elems . pzState $ pz
where len = puzzleSize pz
-- Find the position of the blank
blankPos :: Eq a => Puzzle a -> Point
blankPos pz =
fst . fromJust . find (\(i, tile) -> tile == (blank pz)) . assocs . pzState $ pz
fst . fromJust . find (\(i, tile) -> tile == (blank pz)) . A.assocs . pzState $ pz
-- Get the legal neighbouring positions
neighbourPos :: Int -> Point -> [Point]
neighbourPos len p@(x, y) =
filter (\(x',y') -> and [x' >= 1, y' >= 1, x' <= len, y' <= len])
[(x+1,y), (x-1,y), (x,y+1), (x,y-1)]
$ [(x+1,y), (x-1,y), (x,y+1), (x,y-1)]
-- Get the next legal puzzle states
nextStates :: Eq a => Puzzle a -> [Puzzle a]
@ -131,7 +132,7 @@ nextStates pz = map (\p -> Puzzle (blank pz) (swap p blankAt (pzState pz)))
len = puzzleSize pz
blankAt = blankPos pz
-- Make Puzzle an instance of GameState with step cost one
-- Make Puzzle an instance of GameState with unit step cost
instance Eq a => GameState (Puzzle a) where
succs pz = zip (nextStates pz) (repeat 1)
@ -153,7 +154,7 @@ shufflePuzzle n pz =
inversions :: Ord a => Puzzle a -> Int
inversions pz = sum . map (\l -> length . filter (\e -> e < head l) $ (tail l))
. filter ((> 1). length) . tails
. filter (not . (== b)) . elems . pzState $ pz
. filter (not . (== b)) . A.elems . pzState $ pz
where b = blank pz
-- Calculates the puzzle pairty. The puzzle pairty is invariant under legal moves.
@ -180,7 +181,7 @@ solvePuzzle initState goalState hueristic =
wrongTileCount :: Eq a => Puzzle a -> Puzzle a -> Cost
wrongTileCount givenState goalState =
length . filter (\(a, b) -> a /= b)
$ zip (elems . pzState $ givenState) (elems . pzState $ goalState)
$ zip (A.elems . pzState $ givenState) (A.elems . pzState $ goalState)
-- Calculates Manhattan distance between two points
manhattanDistance :: Point -> Point -> Int
@ -191,9 +192,9 @@ manhattanDistance (x1, y1) (x2, y2) = abs (x1 - x2) + abs (y1 - y2)
sumManhattanDistance :: Ord a => Puzzle a -> Puzzle a -> Cost
sumManhattanDistance givenState goalState =
sum . map (\(p, t) -> manhattanDistance p (fromJust . M.lookup t $ revM))
. assocs . pzState $ givenState
. A.assocs . pzState $ givenState
where
revM = M.fromList . map (\(x, y) -> (y, x)) . assocs . pzState $ goalState
revM = M.fromList . map (\(x, y) -> (y, x)) . A.assocs . pzState $ goalState
-- The classic 15 puzzle (http://en.wikipedia.org/wiki/Fifteen_puzzle)
fifteenPuzzle :: IO ()