Building a Tree with inorder and preorder traversal in Python3.x

Question

I am trying to build a tree using the preorder and inorder traversals (list of ints). Here is what I have so far:

def build(preorder, inorder, heap): # Builds tree with the inorder and preorder traversal
    if len(preorder) == 0:
        return None
    root = preorder[0] # Root is first item in preorder
    k = root
    left_count = inorder[(k-1)] # Number of items in left sub-tree
    left_inorder = inorder[0:left_count]
    left_preorder = preorder[1:1+left_count]
    right_inorder = inorder[1+left_count:]
    right_preorder = preorder[1+left_count:]
    return [root, build(left_preorder, left_inorder), build(right_preorder, right_inorder)]

I believe this algorithm is correct, although I could be wrong.

My question is this - at what point do I insert the items into the tree? I have a class written to handle this, I'm just not sure where to insert this call, as the function will operate recursively. Any suggestions for how I should insert the nodes into the tree would be appreciated.

what? I understand the individual words you are saying but I dont understand what you are trying to do ... and your code is not all that enlightening — Joran Beasley, Apr 23 '14 at 23:02
`root = preorder[0]` *is* the place. The rest doesn't look right. — user58697, Apr 23 '14 at 23:07
I'm not sure where to actually insert the call to my class which will make the list item into a node. — somebody, Apr 23 '14 at 23:10

score 1 · Accepted Answer · answered Apr 23 '14 at 23:11

class heap:
     def __init__(self,the_heap):
         self.heap = the_heap
     def getChildren(self,value):
         n = self.heap.index(value)
         return self.heap[2*n+1],self.heap[2*n+2] # i think ...
     def getParent(self,value):
         n = self.heap.index(value)
         if n == 0: return None
         return self.heap[math.floor(n-1/2.0) ] # i think ...
     def traverse(self):
         #do your traversal here just visit each node in the order you want
         pass

the_heap = heap(range(100))

print the_heap.getChildren(2)
print the_heap.getParent(6)

something like that?

Building a Tree with inorder and preorder traversal in Python3.x

1 Answers1