Solution: Invert Binary Tree

Let's solve the Invert Binary Tree problem using the Tree Depth-first Search pattern.


Given the root node of a binary tree, transform the tree by swapping each node’s left and right subtrees, thus creating a mirror image of the original tree. Return the root of the transformed tree.


  • 00\leq Number of nodes in the tree 100\leq 100
  • 1000-1000 \leq Node.value 1000\leq 1000


For this solution, we do a post-order (left, right, parent) traversal of the binary tree. The algorithm is as follows:

  • Perform post-order traversal on the left child of the root node.
  • Perform post-order traversal on the right child of the root node.
  • Swap the left and right children of the root node.

Since we perform a depth-first search traversal, the children of any node are already mirrored even before we return the node itself.

Let’s look at an example below:

Note: In this example, the node at the top of the stack is the current node.

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