finish v6

1 files changed, 23 insertions, 0 deletions

diff --git a/54a-60/58.hs b/54a-60/58.hs
new file mode 100644
index 0000000..896889f
--- /dev/null
+++ b/54a-60/58.hs
@@ -0,0 +1,23 @@
+data Tree a = Empty | Branch a (Tree a) (Tree a) deriving (Show, Eq)
+
+cbalTree :: Int -> [Tree Char]
+
+cbalTree 0 = [Empty]
+cbalTree x
+  | even n = [Branch 'x' lt rt | let st = cbalTree ln, lt <- st, rt <- st]
+  | otherwise = let st1 = cbalTree ln
+                    st2 = cbalTree (n - ln) in
+                    [Branch 'x' lt rt | lt <- st1, rt <- st2] ++
+                    [Branch 'x' lt rt | lt <- st2, rt <- st1]
+    where ln = n `div` 2
+          n = x - 1
+
+symCbalTrees :: Int -> [Tree Char]
+
+symCbalTrees x
+  | even n = [Branch 'x' st $ reverseTree st | st <- cbalTree ln]
+  | otherwise = []
+  where ln = n `div` 2
+        n = x - 1
+        reverseTree Empty = Empty
+        reverseTree (Branch x l r) = Branch x (reverseTree r) (reverseTree l)