adding time complexity

lectures/21_trees_IV/README.md

@@ -80,9 +80,18 @@ $ ./a.out
 Inorder Traversal using Morris Traversal:
 4 2 6 5 7 1 3 9 8
 ```
+### Time and Space Complexity
+
+- Time Complexity: O(N) (each node is visited at most twice)
+
+- Space Complexity: O(1) (no extra space used except for modifying pointers)
 
 ## 21.3 Morris Traversal - Pre Order
 
+To perform preorder traversal:
+
+Print the node before going left instead of after restoring links.
+
 ```cpp
 void preorderTraversal(TreeNode* root) {
       TreeNode *current=root;
@@ -121,6 +130,12 @@ Preorder Traversal using Morris Traversal:
 1 2 4 5 6 7 3 8 9
 ```
 
+### Time and Space Complexity
+
+- Time Complexity: O(N) (each node is visited at most twice)
+
+- Space Complexity: O(1) (no extra space used except for modifying pointers)
+
 ## 21.4 Morris Traversal - Post Order
 
 ```cpp