master-algorithms-py/ebook_src/abstract_structures/queues/queue.py

#!/usr/bin/env python

__author__ = "bt3"


class Queue(object):

    def __init__(self):
        self.in_stack = []
        self.out_stack = []

    def _transfer(self):
        while self.in_stack:
            self.out_stack.append(self.in_stack.pop())

    def enqueue(self, item):
        return self.in_stack.append(item)

    def dequeue(self):
        if not self.out_stack:
            self._transfer()
        if self.out_stack:
            return self.out_stack.pop()
        else:
            return "Queue empty!"

    def size(self):
        return len(self.in_stack) + len(self.out_stack)

    def peek(self):
        if not self.out_stack:
            self._transfer()
        if self.out_stack:
            return self.out_stack[-1]
        else:
            return "Queue empty!"

    def __repr__(self):
        if not self.out_stack:
            self._transfer()
        if self.out_stack:
            return '{}'.format(self.out_stack)
        else:
            return "Queue empty!"

    def isEmpty(self):
        return not (bool(self.in_stack) or bool(self.out_stack))


if __name__ == '__main__':
    queue = Queue()
    print("Is the queue empty? ", queue.isEmpty())
    print("Adding 0 to 10 in the queue...")
    for i in range(10):
        queue.enqueue(i)
    print("Queue size: ", queue.size())
    print("Queue peek : ", queue.peek())
    print("Dequeue...", queue.dequeue())
    print("Queue peek: ", queue.peek())
    print("Is the queue empty? ", queue.isEmpty())

    print("Printing the queue...")
    print(queue)