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.
food for thought
運用recursion的思路，僅實作接到一個node後，反轉他的左右node，然後再把他的左右node丟給self function即可處理完成
C++ solution
TreeNode* invertTree(TreeNode* root) {
if (!root )
return NULL;
TreeNode* temp = root->right;
root->right = root->left;
root->left = temp;
invertTree(root->right);
invertTree(root->left);
return root;
}