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b2e8672f02
* Fix doubly linked list algorithm * Fix bug with insert_at_tail method Create __str__() method for Node class and LinkedList class * Simplify __str__() of LinkedList Returns empty string if there are no elements in the list * Fix description
121 lines
3.4 KiB
Python
121 lines
3.4 KiB
Python
"""
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- A linked list is similar to an array, it holds values. However, links in a linked
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list do not have indexes.
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- This is an example of a double ended, doubly linked list.
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- Each link references the next link and the previous one.
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- A Doubly Linked List (DLL) contains an extra pointer, typically called previous
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pointer, together with next pointer and data which are there in singly linked list.
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- Advantages over SLL - It can be traversed in both forward and backward direction.
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Delete operation is more efficient"""
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class LinkedList:
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"""
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>>> linked_list = LinkedList()
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>>> linked_list.insert_at_head("a")
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>>> linked_list.insert_at_tail("b")
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>>> linked_list.delete_tail()
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'b'
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>>> linked_list.is_empty
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False
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>>> linked_list.delete_head()
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'a'
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>>> linked_list.is_empty
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True
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"""
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def __init__(self):
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self.head = None # First node in list
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self.tail = None # Last node in list
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def __str__(self):
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current = self.head
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nodes = []
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while current is not None:
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nodes.append(current)
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current = current.next
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return " ".join(str(node) for node in nodes)
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def insert_at_head(self, data):
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new_node = Node(data)
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if self.is_empty:
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self.tail = new_node
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self.head = new_node
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else:
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self.head.previous = new_node
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new_node.next = self.head
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self.head = new_node
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def delete_head(self) -> str:
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if self.is_empty:
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return "List is empty"
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head_data = self.head.data
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if self.head.next:
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self.head = self.head.next
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self.head.previous = None
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else: # If there is no next previous node
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self.head = None
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self.tail = None
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return head_data
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def insert_at_tail(self, data):
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new_node = Node(data)
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if self.is_empty:
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self.tail = new_node
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self.head = new_node
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else:
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self.tail.next = new_node
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new_node.previous = self.tail
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self.tail = new_node
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def delete_tail(self) -> str:
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if self.is_empty:
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return "List is empty"
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tail_data = self.tail.data
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if self.tail.previous:
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self.tail = self.tail.previous
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self.tail.next = None
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else: # if there is no previous node
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self.head = None
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self.tail = None
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return tail_data
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def delete(self, data) -> str:
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current = self.head
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while current.data != data: # Find the position to delete
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if current.next:
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current = current.next
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else: # We have reached the end an no value matches
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return "No data matching given value"
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if current == self.head:
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self.delete_head()
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elif current == self.tail:
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self.delete_tail()
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else: # Before: 1 <--> 2(current) <--> 3
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current.previous.next = current.next # 1 --> 3
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current.next.previous = current.previous # 1 <--> 3
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return data
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@property
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def is_empty(self): # return True if the list is empty
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return self.head is None
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class Node:
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def __init__(self, data):
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self.data = data
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self.previous = None
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self.next = None
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def __str__(self):
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return f"{self.data}"
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