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singly_linked_list_queue.py
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singly_linked_list_queue.py
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class QueueEmptyException(Exception):
pass
class SinglyLinkedListQueue:
class _Node:
def __init__(self, val=None, next_node=None):
self.val = val
self.next = next_node
def __init__(self):
self._head = None
self._tail = None
self._size = 0
def get_size(self):
return self._size
def is_empty(self):
return self._size == 0
def enqueue(self, e):
if self._tail is None:
self._tail = self._Node(val=e)
self._head = self._tail
else:
self._tail.next = self._Node(val=e)
self._tail = self._tail.next
self._size += 1
def dequeue(self):
if self.is_empty():
raise QueueEmptyException("cannot dequeue from an empty queue.")
ret = self._head
self._head = self._head.next
if self._head is None:
self._tail = None
self._size -= 1
return ret.val
def get_front(self):
if self.is_empty():
raise QueueEmptyException("cannot get front from an empty queue.")
return self._head.val
def __str__(self):
res = "Queue: head: "
cur = self._head
while cur is not None:
res += str(cur.val) + "->"
cur = cur.next
res += "NULL tail."
return res
def __repr__(self):
return self.__str__()