haskell full binary tree level order traversal

binary_tree_level_traverse.hs

-- see video https://www.youtube.com/watch?v=q0bFTlmmsJI&t=332s
-- Full Binary Tree
-- A Binary Tree is a full binary tree if every node has 0 or 2 children

data Btree a = Leaf a | Node a (Btree a) (Btree a) deriving Show

tr :: Btree Integer
tr_l = Node 1 (Leaf 2) (Leaf 3)
tr_r = Node 4 (Leaf 5) (Leaf 6)
tr = Node 7 tr_l $ Leaf 8

zipWith' f xs [] = xs
zipWith' f [] xs = xs
zipWith' f (x:xs) (y:ys) = f x y : zipWith' f xs ys

levels :: Btree a -> [[a]]
levels (Leaf a) = [[a]]
levels (Node a l r) = [[a]] ++ zipWith' (++) (levels l) (levels r)

see video

Videos:

pretty print tree

Level order traversal with BFS
Level order traversall with all paths
Level order traversall with zipwith
Level order traversall with label tree
Level order traversal of binary tree with fmap