Upload 4.py

4.py

@@ -0,0 +1,121 @@
+class DoublyLinkedBase:
+    class Node:
+        __slots__ = '_element', '_prev', '_next'
+
+        def __init__(self, element, prev, next):
+            self._element = element
+            self._prev = prev
+            self._next = next
+
+    def __init__(self):
+        self._header = self.Node(None, None, None)
+        self._trailer = self.Node(None, None, None)
+        self._header._next = self._trailer
+        self._trailer._prev = self._header
+        self._size = 0
+
+    def __len__(self):
+        return self._size
+
+    def is_empty(self):
+        return self._size == 0
+
+    def _insert_between(self, e, predecessor, successor):
+        newest = self.Node(e, predecessor, successor)
+        predecessor._next = newest
+        successor._prev = newest
+        self._size += 1
+
+    def insert_at_position(self, pos, e):
+        if pos < 1 or pos > self._size + 1:
+            print("Invalid position")
+            return
+
+        current = self._header
+        for _ in range(1, pos):
+            current = current._next
+
+        self._insert_between(e, current, current._next)
+        print("The element", e, "is successfully inserted at position", pos)
+
+    def _delete_node(self, node):
+        predecessor = node._prev
+        successor = node._next
+        predecessor._next = successor
+        successor._prev = predecessor
+        self._size -= 1
+        element = node._element
+        node._prev = node._next = node._element = None
+        return element
+
+    def delete_by_position(self, pos):
+        if pos < 1 or pos > self._size:
+            print("Invalid position")
+            return
+
+        current = self._header._next
+        for _ in range(1, pos):
+            current = current._next
+
+        removed = self._delete_node(current)
+        print("The element", removed, "is successfully removed")
+
+    def display(self):
+        if self.is_empty():
+            print("Doubly linked list is Empty!")
+        else:
+            current = self._header._next
+            print("Elements in Doubly linked list:")
+            while current != self._trailer:
+                print(current._element, "<->", end=" ")
+                current = current._next
+            print("NULL")
+
+
+print("\t\tImplementation of Doubly Linked List ADT")
+print("\t\t---------------------------------------")
+
+dll = DoublyLinkedBase()
+
+while True:
+    print("\n\tOPERATIONS")
+    print("1-Insertion at position")
+    print("2-Delete at position")
+    print("3-Length")
+    print("4-Is Empty")
+    print("5-Display")
+    print("6-Exit")
+
+    try:
+        ch = int(input("Enter your choice: "))
+
+        if ch == 1:
+            value = int(input("Enter an element: "))
+            pos = int(input("Enter position: "))
+            dll.insert_at_position(pos, value)
+
+        elif ch == 2:
+            if dll.is_empty():
+                print("Doubly linked list is empty!")
+            else:
+                pos = int(input("Enter position to delete: "))
+                dll.delete_by_position(pos)
+
+        elif ch == 3:
+            print("Number of elements:", len(dll))
+
+        elif ch == 4:
+            print("Is list empty?", dll.is_empty())
+
+        elif ch == 5:
+            dll.display()
+
+        elif ch == 6:
+            print("Program Exited")
+            break
+
+        else:
+            print("Invalid choice")
+
+    except ValueError:
+        print("Please enter a valid number")