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Doubly-Linked List
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class Node: | |
def __init__(self, key, next=None, prev=None): | |
self.key = key | |
self.next = next | |
self.prev = prev | |
class DoublyLinkedList: | |
def __init__(self, head=None): | |
self.head = None | |
self.tail = None | |
def is_empty(self): | |
return self.head == None | |
def push_back(self, key): | |
node = Node(key) | |
# set next as None | |
if self.tail == None: | |
self.head = node | |
self.tail = node | |
# set prev as None | |
else: | |
self.tail.next = node | |
node.prev = self.tail | |
self.tail = node | |
def pop_back(self): | |
if self.head == None: | |
raise Exception("Empty List") | |
if self.head == self.tail: | |
self.head = None | |
self.tail = None | |
else: | |
self.tail = self.tail.prev | |
self.tail.next = None | |
def add_after(self, node, key): | |
new_node = Node(key) | |
new_node.next = node.next | |
new_node.prev = node | |
node.next = new_node | |
if new_node.next: | |
new_node.next.prev = new_node | |
if self.tail == node: | |
self.tail = new_node | |
def add_before(self, node, key): | |
new_node = Node(key) | |
new_node.next = node | |
new_node.prev = node.prev | |
node.prev = new_node | |
if new_node.prev: | |
new_node.prev.next = new_node | |
if self.head == node: | |
self.head = new_node | |
def __str__(self): | |
lst = "[" | |
node = self.head | |
while node: | |
lst += str(node.key) | |
if node.next: | |
lst += ", " | |
node = node.next | |
return lst + "]" | |
l = DoublyLinkedList() | |
for i in range(5): l.push_back(i) | |
print(l) |
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