Construct Binary tree using dictionary

Question

I have a dictionary of nodes and their children but I am stuck at inserting the children’s nodes to construct a binary tree. I am using the binary tree to get the preorder traversal and inorder traversal.

input:
Each key pair represent: root:(left child, right child) and can be in any order
{6:(None,None), 10:(2,6), 2:(None,None), 3:(14,None),8:(10,3)}

Output Tree

Binary Tree

I wanted the tree to be in class format (e.g. root.left will return 10, root.left.right will return 6. But my code is not looking for the root node which should be 8:(10,3) and collect all children. How can i enhance the code?

class Node:
    def __init__(self, key, left, right):
        self.key= key
        self.left = left
        self.right = right

   # Compare the new key with the left and right node
   def insert(self, key, vals):
        
        if self.key == None:
           self.key = key
           self.left = vals[0]
           self.right = vals[1]
       
        # else if left is equal to key
        elif self.left == key:
           self.key = key
           self.left = vals[0]
           self.right = vals[1]
        
        # else if right is equal to key 
        elif: 
           self.key = key
           self.left = vals[0]
           self.right = vals[1]

Asked By: Gab

||

Source

Answer 1

The data structure they gave you is a perfectly fine way to store a binary tree. There’s no particular need to convert it to objects. You could have a Tree object and have these all be methods of that class, but I’m not sure that’s really better.

from collections import defaultdict

tree = {6:(None,None), 10:(2,6), 2:(None,None), 3:(14,None),8:(10,3)}

def find_root(tree):
    nodes = defaultdict(int)
    for k,(l,r) in tree.items():
        if l:
            nodes[l] += 1
        if r:
            nodes[r] += 1
    for k in tree:
        if k not in nodes:
            return k

def pre_traverse(tree,node):
    if not node:
        return
    print(node)
    if not node in tree:
        return
    pre_traverse(tree,tree[node][0])
    pre_traverse(tree,tree[node][1])

def in_traverse(tree,node):
    if not node:
        return
    if not node in tree:
        print(node)
        return
    in_traverse(tree,tree[node][0])
    print(node)
    in_traverse(tree,tree[node][1])

root = find_root(tree)
print("in-order traversal:")
in_traverse(tree,root)
print("pre-order traversal:")
pre_traverse(tree,root)

Output:

in-order traversal:
2
10
6
8
14
3
pre-order traversal:
8
10
2
6
3
14

Answered By: Tim Roberts

Construct Binary tree using dictionary

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