Haskell

btree_level_order_traversal.hs

-- see video for description: https://www.youtube.com/watch?v=4mrBrJw_tVc&feature=youtu.be
-- (Nodes must be uniq)
import Data.Set
import Data.List.Split (chunksOf)
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 tr_r

all_paths :: Btree a -> [[a]]
all_paths (Leaf a) = [[a]]
all_paths (Node a l r) = (a:) <$> (all_paths l)++(all_paths r)

(!!!) :: Int -> [a] -> Maybe a
(!!!) i xs
        | (i> -1) && (length xs > i) = Just (xs!!i)
        | otherwise = Nothing

longest tr = maximum $ length <$> (all_paths tr)
cutters tr = ((!!!) <$> [0..(longest tr)-1])
lt tr = fromList <$> (chunksOf (length.all_paths $ tr) ((cutters tr) <*> (all_paths tr)))

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