queue.py

from data_structures.node import Node

class Queue:
    def __init__(self):
        self._front = None
        self._back = None

    def is_empty(self):
        return self._front is None and self._back is None

    def count(self):
        if self.is_empty(): return 0
        return self._front.count()

    def peek(self):
        return (None if self.is_empty() else self._front.data)

    def enqueue(self, data):
        node = Node(data)
        if self.is_empty(): self._front = node
        else: self._back.next = node
        self._back = node
        return data

    def dequeue(self):
        if self.is_empty(): return
        temp = self._front
        if self._front == self._back: self._back = None
        self._front = self._front.next
        return temp.data

    def to_array(self):
        if self.is_empty(): return []
        return self._front.to_array([])