[Leetcode 226, Easy] Invert Binary Tree

Problem:

Invert a binary tree.

     4   /   \  2     7 / \   / \1   3 6   9

to

     4   /   \  7     2 / \   / \9   6 3   1

Trivia:
This problem was inspired by this original tweet by Max Howell:

Google: 90% of our engineers use the software you wrote (Homebrew), but you can’t invert a binary tree on a whiteboard so fuck off.

Analysis:

Solutions:

C++:

    TreeNode* invertTree(TreeNode* root) {        if (root == NULL)            return root;        TreeNode* p_left_subtree_root = invertTree(root->left);        TreeNode* p_right_subtree_root = invertTree(root->right);        root->left = p_right_subtree_root;        root->right = p_left_subtree_root;        return root;    }

Java:

Python: