Algorithm – Mirror(tree):
(1) Call Mirror for left-subtree i.e., Mirror(left-subtree)
(2) Call Mirror for right-subtree i.e., Mirror(right-subtree)
(3) Swap left and right subtrees.
temp = left-subtree
left-subtree = right-subtree
right-subtree = temp
Convert a Binary Tree into its Mirror Tree : https://www.geeksforgeeks.org/write-an-efficient-c-function-to-convert-a-tree-into-its-mirror-tree/