adding in order code

lectures/21_trees_IV/inorder_main.cpp

@@ -0,0 +1,53 @@
+#include <iostream>
+
+class TreeNode {
+public:
+    int val;
+    TreeNode* left;
+    TreeNode* right;
+
+    TreeNode(int value) : val(value), left(NULL), right(NULL) {}
+};
+
+void inorderTraversal(TreeNode* root) {
+        TreeNode *current=root;
+        TreeNode *rightmost;
+        while(current!=NULL){
+            if(current->left!=NULL){
+                rightmost=current->left;
+                while(rightmost->right!=NULL && rightmost->right!=current){
+                    rightmost=rightmost->right;
+                }
+                if(rightmost->right==NULL){ /* first time */
+                    rightmost->right=current;
+                    current=current->left;
+                }else{  /* second time */
+		    std::cout << current->val << " ";
+                    rightmost->right=NULL;
+                    current=current->right;
+                }
+            }else{  /* nodes which do not have left child */
+		std::cout << current->val << " ";
+                current=current->right;
+            }
+    }
+    return;
+}
+
+int main() {
+    TreeNode* root = new TreeNode(1);
+    root->left = new TreeNode(2);
+    root->right = new TreeNode(3);
+    root->left->left = new TreeNode(4);
+    root->left->right = new TreeNode(5);
+    root->left->right->left = new TreeNode(6);
+    root->left->right->right = new TreeNode(7);
+    root->right->right = new TreeNode(8);
+    root->right->right->left = new TreeNode(9);
+
+    std::cout << "Inorder Traversal using Morris Traversal:\n";
+    inorderTraversal(root);
+    std::cout << std::endl;
+
+    return 0;
+}