commit deletes

Task/N-queens-problem/Common-Lisp/n-queens-problem.lisp

@@ -1,22 +0,0 @@
-(defun n-queens (n m)
-  (if (= n 1)
-    (loop for x from 1 to m collect (list x))
-    (loop for sol in (n-queens (1- n) m) nconc
-	  (loop for col from 1 to m when
-		(loop for row from 0 to (length sol) for c in sol
-		      always (and (/= col c)
-				  (/= (abs (- c col)) (1+ row)))
-		      finally (return (cons col sol)))
-		collect it))))
-
-(defun show-solution (b n)
-  (loop for i in b do
-	(format t "~{~A~^~}~%"
-		(loop for x from 1 to n collect (if (= x i) "Q " ". "))))
-  (terpri))
-
-(let ((i 0) (n 8))
-  (mapc #'(lambda (s)
-	    (format t "Solution ~a:~%" (incf i))
-	    (show-solution s n))
-	(n-queens n n)))

Task/N-queens-problem/Haskell/n-queens-problem.hs

@@ -1,31 +0,0 @@
-import Control.Monad
-import Data.List
-
--- given n, "queens n" solves the n-queens problem, returning a list of all the
--- safe arrangements. each solution is a list of the columns where the queens are
--- located for each row
-queens :: Int -> [[Int]]
-queens n = map fst $ foldM oneMoreQueen ([],[1..n]) [1..n]  where
-
-  -- foldM :: (Monad m) => (a -> b -> m a) -> a -> [b] -> m a
-  -- foldM folds (from left to right) in the list monad, which is convenient for
-  -- "nondeterminstically" finding "all possible solutions" of something. the
-  -- initial value [] corresponds to the only safe arrangement of queens in 0 rows
-
-  -- 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 1]
-
--- "safe x y n" tests whether a queen at column x is safe from previous
--- queens as recorded in y, at the distance n rows away
-safe x [] n = True
-safe x (c:y) n = and [ x /= c , x /= c + n , x /= c - n , safe x y (n+1)]
-
--- prints what the board looks like for a solution; with an extra newline
-printSolution y = let n = length y in
-  do mapM_ (\x -> putStrLn [if z == x then 'Q' else '.' | z <- [1..n]]) y
-     putStrLn ""
-
--- prints all the solutions for 6 queens
-main = mapM_ printSolution $ queens 6