Morris Traversal Algorithm

Tree/Morris_Traversal.py

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+#   Morris Traversal
+#   Time Complexity = O(n)
+#   Space Complexity = O(1) (Main advantage of using this traversal. Uses only constant space)
+#                              1
+#                             / \
+#                            /   \
+#                           2     3
+#                          /  \
+#                         /    \
+#                        4      5
+#                                \
+#                                 \
+#                                  6
+#              
+#                 Output --> 4 2 5 6 1 3
+
+class TreeNode:
+    def __init__(self, val=0, left=None, right=None):
+        self.val = val
+        self.left = left
+        self.right = right
+
+# Morris-inorder traversal
+def Morris_Traversal(root):
+    morris = []
+    cur = root
+
+    while cur:
+        if cur.left is None:
+            morris.append(cur.val)
+            cur = cur.right
+        else:
+            temp = cur.left
+            while temp.right and temp.right != cur:
+                temp = temp.right
+
+            if temp.right is None:
+                temp.right = cur
+                cur = cur.left
+            else:
+                temp.right = None
+                morris.append(cur.val)
+                cur = cur.right
+
+    return morris
+
+if __name__ == '__main__':
+    print("\033c", end='', flush=True)
+    # Input tree elements
+    root_val = int(input("Enter the value for the root: "))
+    root = TreeNode(root_val)
+
+    print('\n')
+    queue = [root]
+    while queue:
+        current = queue.pop(0)
+        left_val = int(input(f"Enter the value for the left child of {current.val} (Enter -1 for no child): "))
+        if left_val != -1:
+            current.left = TreeNode(left_val)
+            queue.append(current.left)
+        right_val = int(input(f"Enter the value for the right child of {current.val} (Enter -1 for no child): "))
+        if right_val != -1:
+            current.right = TreeNode(right_val)
+            queue.append(current.right)
+        print('\n')
+
+    # Morris Traversal starts
+    morris = Morris_Traversal(root)
+    print(' '.join([str(i) for i in morris]))
+