Invert Binary Tree in Python

Suppose we have a binary tree. our task is to create an inverted binary tree. So if the tree is like below −

The inverted tree will be like

To solve this, we will use a recursive approach

• if the root is null, then return
• swap the left and right pointers
• recursively solve left subtree and right subtree

Example (Python)

Let us see the following implementation to get a better understanding −

 Live Demo

class TreeNode:
   def __init__(self, data, left = None, right = None):
      self.data = data
      self.left = left
      self.right = right
def make_tree(elements):
   Tree = TreeNode(elements[0])
   for element in elements[1:]:
      insert(Tree, element)
   return Tree
def height(root):
   if root is None:
      return 0
   else :
      # Compute the height of left and right subtree
      l_height = height(root.left)
      r_height = height(root.right)
      #Find the greater one, and return it
      if l_height > r_height :
         return l_height+1
      else:
         return r_height+1
def print_given_level(root, level):
   if root is None:
      return
   if level == 1:
      print(root.data,end = ',')
   elif level > 1 :
      print_given_level(root.left , level-1)
      print_given_level(root.right , level-1)
def level_order(root):
   h = height(root)
   for i in range(1, h+1):
      print_given_level(root, i)
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)
class Solution(object):
   def invertTree(self, root):
      """
      :type root: TreeNode
      :rtype: TreeNode
      """
      self.solve(root)
      return root
   def solve(self,root):
      if not root:
         return
      temp = root.left
      root.left = root.right
      root.right = temp
      self.solve(root.left)
      self.solve(root.right)
tree1 = make_tree([1,2,2,3,4,None,3])
ob1 = Solution()
tree2 = ob1.invertTree(tree1)
level_order(tree2)

Input

[1,2,2,3,4,None,3]

Output

1,2,2,3,None,4,3,

Arnab Chakraborty

Updated on: 28-Apr-2020

714 Views

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