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Just another update

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Ingy döt Net 2015-02-20 00:35:01 -05:00
parent a25938f123
commit 00a190b0a6
6591 changed files with 94363 additions and 23227 deletions
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7
Task/N-queens-problem/Haskell/n-queens-problem-1.hs
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@ -15,11 +15,10 @@ queens n = map fst $ foldM oneMoreQueen ([],[1..n]) [1..n] where
-- given a safe arrangement y of queens in the first i rows, and a list of
-- possible choices, "oneMoreQueen y _" returns a list of all the safe
-- arrangements of queens in the first (i+1) rows along with remaining choices
oneMoreQueen (y,d) _ = [ (x:y, d\\[x]) | x <- d, safe x y]
oneMoreQueen (y,d) _ = [(x:y, delete x d) | x <- d, safe x] where
-- "safe x y" tests whether a queen at column x is safe from previous
-- queens as recorded in y
safe x y = and [ x /= c && x /= c + n && x /= c - n | (n,c) <- zip [1..] y]
-- "safe x" tests whether a queen at column x is safe from previous queens
safe x = and [x /= c + n && x /= c - n | (n,c) <- zip [1..] y]
-- prints what the board looks like for a solution; with an extra newline
printSolution y = do

2
Task/N-queens-problem/Haskell/n-queens-problem-2.hs
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@ -7,5 +7,5 @@ main = mapM_ print $ queens 8
queens :: Int -> [[Int]]
queens n = foldM f [] [1..n]
where
f qs k = [q:qs | q <- [1..n] \\ qs, q `notDiag` qs]
f qs _ = [q:qs | q <- [1..n] \\ qs, q `notDiag` qs]
q `notDiag` qs = and [abs (q - qi) /= i | (qi,i) <- qs `zip` [1..]]