chore(CPlusPlus): add in order binary tree Morris traversal (#317)

User can enter the number of nodes and the value for each note as desired with -1 for a NULL node. The program will build the tree and print out the traversal output.

algorithms/CPlusPlus/README.md

@@ -63,6 +63,7 @@
 3. [Level Order Traversal](Trees/level-order-traversal.cpp)
 4. [Depth first Traversal](Trees/pre-in-post-traversal.cpp)
 5. [Binary Search Tree](Trees/binary-search-tree.cpp)
+6. [In order morris traversal](Trees/in-order-morris-traversal.cpp)
 
 # Maths
 1. [Kaprekar Number](Maths/Kaprekar-number.cpp)

algorithms/CPlusPlus/Trees/in-order-morris-traversal.cpp

@@ -0,0 +1,98 @@
+/** 
+ * Conduct a morris in-order traversal of a binary tree,
+ * printing out the value at each node according to 
+ * the traversal using user defined inputs.
+ * Node.val can take any number except -1
+ **/
+# include <iostream>
+# include <vector>
+using namespace std;
+
+// Basic tree definition
+struct Node {
+    int val;
+    Node* left;
+    Node* right;
+    Node(int x) : val(x), left(nullptr), right(nullptr) {};
+
+};
+
+/**
+ * Print out the values of the treenodes using an in-order traversal
+ * (left subtree - root - right subtree) without using additional memory
+ * node values are printed with a space between the values of each 2 nodes
+ **/
+
+void print_morris(Node* root) {
+    if (!root) cout << "\n";
+
+    Node* previous;
+
+    while(root) {
+        if (!root->left) {
+            cout << root->val << " ";
+            root = root->right;
+        } else {
+            previous = root->left;
+
+            while (previous->right && previous->right != root) 
+                previous = previous->right;
+
+            if (!previous->right) {
+                previous->right = root;
+                root = root->left;
+            } else {
+                previous->right = NULL;
+                cout << root->val << " ";
+                root = root->right;
+            }
+        }
+    }
+}
+
+Node* build_tree(vector<int>& nodes, Node* root, int i, int n) {
+    if (i < n) {
+        if (nodes[i] == -1) return NULL;
+        Node* temp = new Node(nodes[i]);
+        root = temp;
+
+        root->left = build_tree(nodes, root->left, 2 * i + 1, n);
+        root->right = build_tree(nodes, root->right, 2 * i + 2, n);
+    }
+    return root;
+}
+
+int main() {
+    vector<int> nodes;
+    int numNodes;
+
+    cout << "Enter the number of nodes: ";
+    cin >> numNodes;
+    if (!numNodes) { cout << "\n"; return 0; }
+
+    for (int i = 0; i < numNodes; i++) {
+        cout << "Enter the value for node followed by ENTER (-1 for no node) " << i + 1 << ": ";
+        int nodeVal;
+        cin >> nodeVal;
+        nodes.push_back(nodeVal);
+    }
+
+    Node* my_root = build_tree(nodes, my_root, 0, nodes.size());
+
+    /**
+     * Test for the morris traversal:
+     * tree referenced by my_root:
+     *              8
+     *            /   \
+     *           5    10
+     *               /  \
+     *              9    6
+     * 
+     * for input:7, 8 5 10 -1 -1 9 6
+     * expected output: 5 8 9 10 6
+     * time complexity: O(n), space complexity O(1)
+     **/
+
+    print_morris(my_root);
+    return 0;
+}