level order traversal with bfs

level_order_btree_bfs.hs

-- see video https://www.youtube.com/watch?v=OibwXW1ssV8
-- pretty print tree https://www.youtube.com/watch?v=Ud-1Z0hBlB8

data Btree a = Empty | Node a (Btree a) (Btree a) deriving Show
tr_l = Node "b" (Node "d" Empty Empty) (Node "e" Empty Empty)
tr_r = Node "c" (Node "f" Empty Empty) (Node "g" Empty Empty)
--tr = Node "a" tr_l tr_r :: Btree String
tr_ll = Node "x" tr_l Empty
tr = Node "a" tr_ll tr_r :: Btree String

lev_ord t = lo [t]
  where lo :: [Btree a] -> [a]
        lo [] = []
        lo (Empty:xs) = lo xs
        lo (Node v l r:xs) = v : lo (xs ++ [l,r])

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