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Back to Eight_Queens_puzzle_(Haskell)

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queens

queens :: Int -> [[Int]]
queens n = foldM f [] [1..n] where
    f rows _ = [row : rows |
                row <- [1..n],
                safeAddition rows row 1]


safeAddition

safeAddition :: [Int] -> Int -> Int -> Bool
safeAddition [] _ _ = True
safeAddition (r:rows) row i =
   row /= r &&
   abs (row - r) /= i &&
   safeAddition rows row (i + 1)


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