class FavoritesList:
class _Item:
__slots__ = '_value', '_count'
def __init__(self, v):
self._value = v
self._count = 0
def _find_position(self, e):
""" Search for element e and return its Position """
walk = self._data.first()
while walk is not None and walk.element()._value != e:
walk = self._data.after(walk)
return walk
def _move_up(self, p):
""" Move item at Position p earlier in the list based on access count """
if p != self._data.first():
walk = self._data.before(p)
cnt = p.element()._count
if cnt > walk.element()._count:
while walk != self._data.first() and cnt > self._data.before(
walk).element()._count:
walk = self._data.before(walk)
self._data.add_before(walk, self._data.delete(p))
""" ==================================Public Methods==================================== """
def __init__(self):
self._data = PositionalList()
def __len__(self):
return len(self._data)
def is_empty(self):
return self._data.is_empty()
def access(self, e):
""" Access element e, thereby increasing its access count """
p = self._find_position(e)
if p is None:
p = self._data.add_last(self._Item(e))
p.element()._count += 1
self._move_up(p)
def remove(self, e):
p = self._find_position(e)
if p is not None:
self._data.delete(p)
def top(self, k):
if not 1 <= k <= len(self):
raise ValueError("Illegal value for k")
walk = self._data.first()
for _ in range(k):
item = walk.element()._value
yield item
walk = self._data.after(walk)
class UnsortedPriorityQueue(PriorityQueueBase):
"""A min-oriented priority queue implemented with an unsorted list"""
def __init__(self):
self._data = PositionalList()
def _find_min(self):
"""Return Position of item with minimum key"""
if self._data.is_empty(): # empty queue
raise ValueError("Empty Priority Queue")
small = self._data.first()
walk = self._data.after(small)
while walk != None:
# find a item with smaller key or higher priority
if small.element() > walk.element():
small = walk
walk = self._data.after(walk)
return small
def __len__(self):
return len(self._data)
def add(self, key, value):
"""Add a key-value pair"""
self._data.add_last(self._Item(key, value))
def min(self):
"""Return but do not remove (k,v) tuple with minimum key"""
item = self._find_min().element()
return item._key, item._value
def remove_min(self):
"""Remove and return (k,v) tuple with minimum key"""
p = self._find_min() # find the position
item = self._data.delete(
p) # delete the position and return the element
return item._key, item._value