[Haskell-beginners] How to delete a range from AVL tree.
Alexander.Vladislav.Popov
alexander.vladislav.popov at gmail.com
Thu Sep 16 13:12:12 EDT 2010
Hi.
Help me to solve the problem I faced with.
I'm trying to delete items from the AVL tree 'itree' that are between 0 and 2.
But as you can see the result tree contains value of 1.
> import Data.Tree.AVL
> import Data.COrdering
> mydelete' :: (Ord a) => a -> a -> AVL a -> AVL a
> mydelete' p1 p2 tree = let res = delete cmp tree in
> case contains res cmp of
> True -> mydelete' p1 p2 res
> otherwise -> res
> where
> cmp = between p1 p2
> between a b x = if x < a
> then LT
> else if x > b
> then GT
> else EQ
> itree = push ((sndByCC compare) 3) 3 (pair 1 2)
> idel = mydelete' 0 2
*Main> idel itree
P (Z E 1 E) 3 E
*Main> idel $ idel itree
P (Z E 1 E) 3 E
*Main>
Explain me why I got following results and where I made error.
*Main> (mydelete' 0 3) itree
E
*Main> (mydelete' 0 2) itree
P (Z E 1 E) 3 E
*Main> (mydelete' 1 2) itree
P (Z E 1 E) 3 E
*Main> (mydelete' 1 1) itree
Z (Z E 1 E) 2 (Z E 3 E)
*Main> (mydelete' 2 1) itree
Z (Z E 1 E) 2 (Z E 3 E)
*Main> (mydelete' 0 1) itree
Z (Z E 1 E) 2 (Z E 3 E)
*Main> (mydelete' 0 2) itree
P (Z E 1 E) 3 E
*Main> (mydelete' (-1) 2) itree
P (Z E 1 E) 3 E
Alexander
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