Construct String from Binary Tree in Python

Suppose we have a binary tree we have to make a string consists of parenthesis and integers from a binary tree with the preorder traversing way. A null node will be represented by empty parenthesis pair "()". And we need to omit all the empty parenthesis pairs that don't affect the one-to-one mapping relationship between the string and the original binary tree.

So, if the input is like

then the output will be 5(6()(8))(7)

To solve this, we will follow these steps −

• ans := blank string
• Define a function pot(). This will take node, s
• if is null, then
  • return blank string
• if if left or right of node is null, then
  • return node.data
• ss := node.data
• if node.left is not null, then
  • ss := ss concatenate '(' concatenate pot(node.left, blank string) concatenate ')'
• otherwise,
  • ss := ss concatenate '()'
• if node.right is not null, then
  • ss := ss concatenate '(' concatenate pot(node.right, blank string) concatenate ')'
• return ss
• From the main method do the following −
• return pot(t, blank string)

Let us see the following implementation to get better understanding −

Example

 Live Demo

class TreeNode:
   def __init__(self, data, left = None, right = None):
      self.data = data
      self.left = left
      self.right = right
def insert(temp,data):
      que = []
      que.append(temp)
      while (len(que)):
         temp = que[0]
         que.pop(0)
         if (not temp.left):
            if data is not None:
               temp.left = TreeNode(data)
            else:
               temp.left = TreeNode(0)
            break
         else:
            que.append(temp.left)
         if (not temp.right):
            if data is not None:
               temp.right = TreeNode(data)
            else:
               temp.right = TreeNode(0)
            break
         else:
            que.append(temp.right)
def make_tree(elements):
   Tree = TreeNode(elements[0])
   for element in elements[1:]:
      insert(Tree, element)
   return Tree
class Solution:
   def tree2str(self, t: TreeNode):
      ans = ''
      def pot(node, s):
         if node == None or node.data == 0:
            return ''
         if node.left == node.right == None:
            return str(node.data)
         ss = str(node.data)
         if node.left != None:
            ss = ss + '(' + pot(node.left, '') + ')'
         else:
            ss = ss + '()'
         if node.right != None:
            ss = ss + '(' + pot(node.right, '') + ')'
         return ss
      return pot(t, '')
ob = Solution()
root = make_tree([5,6,7,None,8])
print(ob.tree2str(root))

Input

[5,6,7,None,8]

Output

5(6()(8))(7)