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doubly-linked-list.py
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doubly-linked-list.py
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class Node:
def __init__(self, data, prev):
self.data = data
self.prev = prev
self.next = None
class DoublyLinkedList:
"""
A doubly-linked list data structure, where each node in the list contains references
for both the node before it and the node after it.
"""
def __init__(self):
self.head = None
self.tail = None
def add(self, element):
"""Adds an element to the tail end of the list."""
if self.tail:
self.tail.next = Node(element, prev=self.tail)
self.tail = self.tail.next
else:
self.head = Node(element, prev=None)
self.tail = self.head
def remove(self, element):
"""Removes all occurrences of the given element from the list."""
if self.head:
# Remove as many heads as necessary
while self.head.data == element:
self.head = self.head.next
self.head.prev = None
# Remove as many tails as necessary
while self.tail.data == element:
self.tail = self.tail.prev
self.tail.next = None
# Iterate through rest of list
current_node = self.head.next
while current_node.next:
if current_node.data == element:
# Link adjacent nodes
current_node.prev.next = current_node.next
current_node.next.prev = current_node.prev
current_node = current_node.next
else:
return None
def clear(self):
"""Clears the contents of the list."""
self.head = self.tail = None
def reverse(self):
"""Reverses the list in place (or returns `None` if the list is empty)."""
if self.head:
self.head = self.tail
current_node = self.head
while current_node.prev:
# Swap adjacent nodes
old_prev = current_node.prev
current_node.prev = current_node.next
current_node.next = old_prev
current_node = current_node.next
# Set new tail
self.tail = current_node
self.tail.prev = self.tail.next
self.tail.next = None
else:
return None