Resume
I found an interesting algorithm to find the max and sum of a tree in Haskell using map. This algorithm is pretty short and useful for me.
Type definition
data Tree = Leaf Int | Node [Tree]In the definition above, we defined a tree. In the tree, we will have either a Leaf Int or a Node [Tree].
Attention: this is not a binary tree. It can have many sub-nodes within a node.
Sum
sum' :: Tree -> Int
sum' (Leaf l) = l
sum' (Node node) = sum (map sum' node)We use a map to calculate every value of a Leaf in the tree, then construct a list with these values. Finally, we can figure out the sum of the tree.
Max
max' :: Tree -> Int
max' (Leaf l) = l
max' (Node node) = maximum (map max' node)Like sum above, we can reuse it without major modification. Just replace sum with maximum. Then this function will figure out the maximum value of this tree recursively.
Test
let tree = Node [Node [Leaf 4, Leaf 5], Leaf 6]
*Main> let tree = Node [Node [Leaf 4, Leaf 5], Leaf 6]
*Main> sum' tree
15
*Main> max' tree
6
