3 files changed, 30 insertions, 0 deletions
diff --git a/11-20/11.hs b/11-20/11.hs
new file mode 100644
index 0000000..a64fdc2
--- /dev/null
+++ b/11-20/11.hs
@@ -0,0 +1,14 @@
+pack :: Eq a => [a] -> [[a]]
+
+pack [] = []
+pack [x] = [[x]]
+pack (x:xs) = if x == head y then (x:y):ys else [x]:(y:ys) where (y:ys) = pack xs
+
+data ListItem a = Single a | Multiple Int a deriving Show
+encodeModified :: Eq a => [a] -> [ListItem a]
+
+encodeModified xs = map (\x -> let l = length x
+                                   h = head x in
+                           case l of
+                             1 -> Single h
+                             otherwise -> Multiple l h) $ pack xs
diff --git a/11-20/12.hs b/11-20/12.hs
new file mode 100644
index 0000000..3c1ce90
--- /dev/null
+++ b/11-20/12.hs
@@ -0,0 +1,6 @@
+data ListItem a = Single a | Multiple Int a deriving Show
+decodeModified :: [ListItem a] -> [a]
+
+decodeModified [] = []
+decodeModified (Single x:xs) = x:(decodeModified xs)
+decodeModified (Multiple l x:xs) = replicate l x ++ decodeModified xs
diff --git a/11-20/13.hs b/11-20/13.hs
new file mode 100644
index 0000000..db5509e
--- /dev/null
+++ b/11-20/13.hs
@@ -0,0 +1,10 @@
+data ListItem a = Single a | Multiple Int a deriving Show
+encodeDirect :: Eq a => [a] -> [ListItem a]
+
+encodeDirect [] = []
+encodeDirect [x] = [Single x]
+encodeDirect (x:xs) = if x == h then n:ys else (Single x):(y:ys)
+    where (y:ys) = encodeDirect xs
+          helper (Single z) = (Multiple 2 z, z)
+          helper (Multiple c z) = (Multiple (c + 1) z, z)
+          (n, h) = helper y