Hi Tom
data Tree = Branch Tree Tree | Leaf Int deriving (Eq, Ord)
leaves :: Tree -> Set Int
leaves (Leaf n) = singleton n
leaves (Branch left right) = union (leaves left) (leaves right)
The standard method for a traversal over leaves with accumulation is:
leaves :: Tree -> Set Int
leaves x = f []
where
f (Leaf n) rest = n : rest
f (Branch l r) rest = f l (f r rest)
This makes the construction of the list quite cheap.
Then you can do the fromList trick, and that might give you a speed up.
Thanks
Neil
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