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Today's Topics:
1. [Q] Bulding an Array of Tree Nodes (Chul-Woong Yang)
----------------------------------------------------------------------
Message: 1
Date: Wed, 19 Oct 2016 11:11:40 +0900
From: Chul-Woong Yang <cwy...@aranetworks.com>
To: Haskell-Beginners <beginners@haskell.org>
Subject: [Haskell-beginners] [Q] Bulding an Array of Tree Nodes
Message-ID:
<CALmycjo7u5huwdLuHmx=_qsuj=agwkprizrqxk5hsbsszqs...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Hi, all.
I need to make graph/tree structure,
the nodes of which are contained in _array_
to facilitate random access to that node.
There is no problem in building an array of graph nodes from edge list.
> -- Graphs
> data Graph a = GNode a [Graph a]
> mkGraph :: [(a,[Int])] -> Array Int (Graph a)
> mkGraph table = table'
> where n = length table
> table' = listArray (0,n-1) $
> map(\(x,adjs) -> GNode x (map (table' !) adjs)) table
However, I cannot build tree from the same input,
if given edge list is undirected one.
The leaf node's edge has a link to parent node
when edge list is undirected, and I cannot find way
to cut that parent edge in building tree.
For example, think of following simple tree:
A(0)
/ \
B(1) C(2)
It's hard to build tree with following edge list:
[('A',[1,2]),
('B',[0]),
('C',[0])]
but it's easy when edge list is following:
[('A',[1,2]),
('B',[]),
('C',[])]
How can I build an array of tree nodes for the former?
In other words, How can I build following mkTree function?
data Tree a = Node { value :: a
, parent :: Tree a
, level :: Int
, children :: [Tree a]
} deriving Show
mkTree :: [(a,[Int])] -> Array Int (Tree a)
Any comments or helps will be deeply appreciated.
Thank you.
Chul-Woong Yang
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