Program to invert a binary tree in Python

Suppose we have a binary tree root, we have to invert it so that its left subtree and right subtree are exchanged and their children are also exchanged recursively.

So, if the input is like

then the output will be

To solve this, we will follow these steps −

• Define a method solve(), this will take node

• if root is null, then

  • return

• left of root := solve(right of root)

• right of root := solve(right of root)

• return root

Let us see the following implementation to get better understanding −

Example

class TreeNode:
   def __init__(self, value):
      self.val = value
      self.left = None
      self.right = None

def inorder(root):
   if root:
      inorder(root.left)
      print(root.val, end=', ')
      inorder(root.right)

class Solution:
   def solve(self, root):
   if not root:
      return
   root.left, root.right = self.solve(root.right), self.solve(root.left)
   return root

ob = Solution()
root = TreeNode(5)
root.left = TreeNode(4)
root.right = TreeNode(10)
root.right.left = TreeNode(7)
root.right.right = TreeNode(15)
inv = ob.solve(root)
inorder(inv)

Input

root = TreeNode(5)
root.left = TreeNode(4)
root.right = TreeNode(10)
root.right.left = TreeNode(7)
root.right.right = TreeNode(15)

Output

15, 10, 7, 5, 4,