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Decode the Coding Interview in Python: Real-World Examples

Invert Binary Tree

Explore how to invert a binary tree by swapping its left and right subtrees using depth-first search. Understand the time complexity of O(n) and space complexity considerations, helping you master tree transformations essential for coding interviews.

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Description

In this lesson, your task is to invert a given a binary tree, T.

Let’s look at an example below:

Coding exercise

Python 3.5
from TreeNode import *
def invert_tree(root):
  pass
Invert binary tree

Solution

We can solve this problem using depth-first search (DFS).

The inverse of an empty tree is the empty tree. To invert tree T with root and subtrees left and right, we keep root the same and invert the right and left subtrees.

Let’s review the implementation below:

Python 3.5
from TreeNode import *
def invert_tree(root):
    if root is None: 
      return root
    right = invert_tree(root.right);
    left = invert_tree(root.left);
    root.left = right;
    root.right = left;
    return root;
# Driver Code
root = TreeNode(1)
root.left = TreeNode(2)
root.right = TreeNode(3)
root.left.left = TreeNode(4)
root.left.right = TreeNode(5)
root.right.left = TreeNode(6)
root.right.right = TreeNode(7)
print_tree(invert_tree(root))
Invert binary tree

Complexity measures

Time Complexity Space Complexity
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