class Scoreboard(object):
""" Fixed-length sequence of high scores in nondecreasing order."""
def __init__(self, capacity=10):
""" Initialize scoreboard with given maximum capacity."""
self._board = SinglyLinkedList()
self._cap = capacity
def __len__(self):
return len(self._board)
def __getitem__(self, k):
""" Return entry index k."""
if k == 0:
return self._board.head()
if k == len(self) - 1:
return self._board.tail()
if k > len(self) - 1 or k < 0:
raise IndexError('Index is out of range')
else:
walk = self._board._head
for _ in range(k):
walk = walk._next
return walk._element
def add(self, entry):
""" Consider adding entry to high scores."""
score = entry.get_score()
# insert first element
if len(self) == 0:
self._board.add_first(entry)
return
good = score > self._board.head().get_score() or len(self) < self._cap
if good:
# insert an element to self._board
prev = walk = self._board._head
while walk is not None:
if walk._element.get_score() > score:
break
else:
prev = walk
walk = walk._next
prev._next = self._board._Node(entry, walk)
self._board._size += 1
if walk is None:
self._board._tail = prev._next
# make the lenght of self._board to capacity
if len(self) > self._cap:
self._board.remove_first()
return
def __repr__(self):
""" String representation of the scoreboard."""
s = ''
walk = self._board._head
while walk is not None:
s += str(walk._element.get_score()) + ','
walk = walk._next
return s[:-1]
class LeakyStack(object):
""" Implementation of a leaky stack based on singly linked list.
When push is invoked with the stack at full capacity, accept the pushed
element at the top while “leaking” the oldest element from the bottom of
the stack to make room.
"""
def __init__(self, maxlen):
super(LeakyStack, self).__init__()
self._maxlen = maxlen
self._data = SinglyLinkedList()
self._size = 0
def __len__(self):
"""Return the number of elements in the stack."""
return self._size
def is_empty(self):
"""Return True if the stack is empty."""
return self._size == 0
def push(self, e):
"""Add element e to the top of the stack.
When stack is full, drop the bottom element to make room for new
element.
"""
self._data.add_first(e)
if self._size < self._maxlen:
self._size += 1
elif self._size <= len(self._data) // 2:
self._resize()
def _resize(self):
""" Delete the elements that not in the stack."""
self._data.cut(self._size)
def pop(self):
"""Remove and return the element from the top of the stack (i.e.,
LIFO).
Raise Empty exception if the stack is empty.
"""
if self.is_empty():
raise Empty('Leaky stack is empty!')
rlt = self._data.remove_first()
self._size -= 1
return rlt
def top(self):
""" Return (but do not remove) the element at the top of the stack.
Raise Empty exception if the stack is empty.
"""
if self.is_empty():
raise Empty('Leaky stack is empty!')
return self._data.head()
