0

This is my python code to make an Ordered Binary Decision Diagram (not very relevant for the context). So I just have a tree of a particular height, and I need to set some of the leaf nodes to one. So I have a variable path which involves an array of "decisions", to go left or right from that particular node. But my code is by mistake modifying multiple roots. I am fairly new to Python and I used to rely on pointers when I used C. 

def makeCubes(arr):
        ans = []
        for ar in arr:
            ar2 = [ar[i:i + 2] for i in range(0, len(ar), 2)] 
            #splitting into segments of 2 each
            if not '00' in ar2:
                ans += [ar2]
        return ans

class Node:
    def __init__(self,key):
        self.key = key
        self.left = None
        self.right = None
    def addLeft(self,node):
        self.left = node
    def addRight(self,node):
        self.right = node

def makeTree(size):
    if(size == 1):
        leaf = Node('x0')
        leaf.addLeft(Node('zero'))
        leaf.addRight(Node('zero'))
        return leaf
    else:
        node = Node('x'+str(size-1))
        childNode = makeTree(size-1)
        node.addLeft(childNode)
        node.addRight(childNode)
        return node

def inOrder(root):
    if(root != None):
        return inOrder(root.left) + [root.key] + inOrder(root.right)
    return []

def makeOBDD(array):
    maxLen = max([len(word) for word in array])
    tree = makeTree(maxLen)
    for cube in array:
        tree = makeOne(tree,cube)
    return tree

def makeOne(root,cube):
    print("cube",cube)
    if(cube == []):
        print("updated")
        root.key = 'one'        
    else:
        element = cube[0]
        if(element == '01'):
            root.addLeft(makeOne(root.left,cube[1:]))
        elif(element == '10'):
            root.addRight(makeOne(root.right,cube[1:]))
    return root

# ab + a'b'
'''
Expected output
   x1
  /  \
 x0   x0
/ \   / \ 
1  0  0  1
'''
cubeSet = ['1010','0101']
cubes = makeCubes(cubeSet)
print(cubes)
obdd = makeOBDD(cubes)
print(inOrder(obdd))
0 _
  • 10,524
  • 11
  • 77
  • 109
Vighnesh Velayudhan
  • 23
  • 1
  • 8
  • I see your expected output, could you share the output you are getting right now as well? – OmegaNalphA Sep 05 '17 at 18:54
  • Oh I was getting the entire leaves to be 1. Finally figured out that while making the tree I made the same `childNode` as the child to both left and right(in `makeTree()` so all my updates happened twice... – Vighnesh Velayudhan Sep 07 '17 at 04:41
  • What are the cubes supposed to mean here? In the context of BDDs, "cube" is usually used to mean an assignment of Boolean values to some of the variables (quoting from Fabio Somenzi's ["Binary Decision Diagram's](http://www.ecs.umass.edu/ece/labs/vlsicad/ece667/reading/somenzi99bdd.pdf): "The path actually identifies a cube of the function, that is the conjunction of some variables or their complements."). – 0 _ Oct 15 '17 at 20:19

0 Answers0