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| -rw-r--r-- | 90-94/90.hs | 18 |
1 files changed, 18 insertions, 0 deletions
diff --git a/90-94/90.hs b/90-94/90.hs new file mode 100644 index 0000000..a634409 --- /dev/null +++ b/90-94/90.hs @@ -0,0 +1,18 @@ +import Data.Bits (shift, (.|.), (.&.), Bits) + +queens :: Int -> [[Int]] + +queens n = q 0 0 0 0 + where q :: Int -> Int -> Int -> Int -> [[Int]] + q s l r d + | s == n = return [] + | otherwise = do i <- [0..n-1] + let p = shift 1 i + if p.&.forb == 0 then + map (i:) (q (s + 1) + (shift (l.|.p) (-1)) + ((shift (r.|.p) 1).&.mask) + (d.|.p)) + else [] + where forb = l.|.r.|.d + mask = (shift 1 n) - 1 |