def invertTree(root: TreeNode) -> TreeNode:
if not root:
return None
root.left, root.right = invertTree(root.right), invertTree(root.left)
return root
def mergeTrees(t1: TreeNode, t2: TreeNode) -> TreeNode:
if not t1:
return t2
if not t2:
return t1
t1.left = mergeTrees(t1.left, t2.left)
t1.right = mergeTrees(t1.right, t2.right)
t1.val += t2.val
return t1