class SortedPriorityQueue(PriorityQueueBase):
"""A min-oriented priority queue implemented with a sorted list."""
def __init__(self):
"""Create a new empty Priority Queue."""
self._data = PositionalList()
def __len__(self):
"""Return the number of items in the priority queue."""
return len(self._data)
def add(self, key, value):
"""Add a key-value pair."""
newest = self._Item(key, value)
walk = self._data.last() # walk backward looking for smaller key
while walk is not None and newest < walk.element():
walk = self._data.before(walk)
if walk is None:
self._data.add_first(newest) # new key is the smallest
else:
self._data.add_after(walk, newest) # newest goes after walk
def min(self):
"""Return but do not remove (k, v) tuple with minimum key."""
if self.is_empty():
raise Empty('Priority queue is empty.')
p = self._data.first()
item = p.element()
return (item._key, item._value)
def remove_min(self):
"""Remove and return (k, v) tuple with minimum key from the priority queue."""
if self.is_empty():
raise Empty('Priority queue is empty.')
item = self._data.delete(self._data.first())
return (item._key, item._value)
def test_first_returns_first_Position_in_the_list(self):
pl = PositionalList()
n = PositionalList._Node('foo', pl._header, pl._trailer)
pl._header._next = n
pl._trailer._prev = n
expected_position = PositionalList.Position(pl, n)
result_position = pl.first()
self.assertEqual(result_position, expected_position)