def test_add_last_inserts_element_at_back_and_returns_Position(self):
pl = PositionalList()
element = 'foo'
result_position = pl.add_last(element)
self.assertIs(result_position._node._element, element)
self.assertIs(result_position._node._next, pl._trailer)
self.assertIs(pl._trailer._prev, result_position._node)
class UnsortedPriorityQueue(PriorityQueueBase):
"""A min-oriented priority queue implemented with an unsorted list."""
def _find_min(self):
"""Return Position of item with minimum key."""
if self.is_empty():
raise Empty('Priority queue is empty')
small = self._data.first()
walk = self._data.after(small)
while walk is not None:
if walk.element() < small.element():
small = walk
walk = self._data.after(walk)
return small
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."""
self._data.add_last(self._Item(key, value))
def min(self):
"""Return but do not remove (k, v) tuple with minimum key."""
p = self._find_min()
item = p.element()
return (item._key, item._value)
def remove_min(self):
"""Remove and return (k, v) tuple with minimum key from the prioriry queue."""
p = self._find_min()
item = self._data.delete(p)
return (item._key, item._value)