queue.py

#!/usr/bin/env python3

from nodes import SLLNode

class Queue:

    def __init__(self):
        self.head = None
        self.tail = None
        self.size = 0

    def enqueue(self, data):
        node = SLLNode(data)
        if self.head is None:
            self.head = self.tail = node
        else:
            self.tail.next = node
            self.tail = node
        self.size += 1

    def dequeue(self):
        if self.head is not None:
            data = self.head.data
            self.head = self.head.next
            self.size -= 1
            return data
        else:
            raise Exception('Queue is empty')

    def peek(self):
        if self.head is not None:
            return self.head.data
        else:
            raise Exception('Queue is empty')

    def isempty(self):
        return self.size == 0


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