bag

# -*- coding: utf-8 -*-
"""
Created on Tue Feb 19 15:48:58 2019

@author: Zsu
"""


class Bag:
    # creates a new, empty Bag
    def __init__(self):
        self.__bag = []

    # adds a new element to the Bag
    # O(1)
    def add(self, e):
        self.__bag.append(e)

    # removes one occurrence of an element from a Bag
    # returns True if an element was actually removed (the Bag contained the element e), or False if nothing was removed
    # O(n)
    def remove(self, e):
        if self.search(e):
            self.__bag.remove(e)
            return True

        return False

    # searches for an element e in the Bag
    # returns True if the Bag contains the element, False otherwise
    # O(n)
    def search(self, e):
        return e in self.__bag

    # counts and returns the number of times the element e appears in the bag
    # O(n)
    def nrOccurrences(self, e):
        return self.__bag.count(e)

    # returns the size of the Bag (the number of elements)
    # O(1)
    def size(self):
        return len(self.__bag)

    # returns True if the Bag is empty, False otherwise
    # O(1)
    def isEmpty(self):
        return not self.__bag

    # returns a BagIterator for the Bag
    # O(1)
    def iterator(self):
        return BagIterator(self.__bag)


class BagIterator:
    #creates an iterator for the Bag b, set to the first element of the bag, or invalid if the Bag is empty
    def __init__(self, b):
        self.__bag = b
        self.__i = 0

    # returns True if the iterator is valid
    # O(1)
    def valid(self):
        return self.__i < len(self.__bag)

    # returns the current element from the iterator.
    # throws ValueError if the iterator is not valid
    # O(1)
    def getCurrent(self):
        if not self.valid():
            raise ValueError("Iterator not valid")

        return self.__bag[self.__i]

    # moves the iterator to the next element
    # throws ValueError if the iterator is not valid
    # O(1)
    def next(self):
        if not self.valid():
            raise ValueError("Iterator not valid")

        self.__i += 1

    # sets the iterator to the first element from the Bag
    # O(1)
    def first(self):
        self.__i = 0