A-M baby

Task/Longest-common-subsequence/Haskell/longest-common-subsequence-1.hs

@@ -0,0 +1,7 @@
+longest xs ys = if length xs > length ys then xs else ys
+
+lcs [] _ = []
+lcs _ [] = []
+lcs (x:xs) (y:ys)
+  | x == y    = x : lcs xs ys
+  | otherwise = longest (lcs (x:xs) ys) (lcs xs (y:ys))

Task/Longest-common-subsequence/Haskell/longest-common-subsequence-2.hs

@@ -0,0 +1,12 @@
+import Data.Array
+
+lcs xs ys = a!(0,0) where
+  n = length xs
+  m = length ys
+  a = array ((0,0),(n,m)) $ l1 ++ l2 ++ l3
+  l1 = [((i,m),[]) | i <- [0..n]]
+  l2 = [((n,j),[]) | j <- [0..m]]
+  l3 = [((i,j), f x y i j) | (x,i) <- zip xs [0..], (y,j) <- zip ys [0..]]
+  f x y i j
+    | x == y    = x : a!(i+1,j+1)
+    | otherwise = longest (a!(i,j+1)) (a!(i+1,j))

Task/Longest-common-subsequence/Haskell/longest-common-subsequence-3.hs

@@ -0,0 +1,2 @@
+*Main> lcs "thisisatest" "testing123testing"
+"tsitest"

Task/Longest-common-subsequence/Haskell/longest-common-subsequence-4.hs

@@ -0,0 +1,10 @@
+import Data.List
+
+longest xs ys = if length xs > length ys then xs else ys
+
+lcs xs ys = head $ foldr(\xs -> map head. scanr1 f. zipWith (\x y -> [x,y]) xs) e m where
+    m = map (\x -> flip (++) [[]] $ map (\y -> [x | x==y]) ys) xs
+    e = replicate (length ys) []
+    f [a,b] [c,d]
+     | null a = longest b c: [b]
+     | otherwise = (a++d):[b]