def last(self):
if self.is_empty():
raise EmptyError('Queue is empty')
# 最后一个数据保的位置, 比队尾空位置提前一个索引
last_idx = (self._front + self._size - 1) % self.capacity
return self._data[last_idx]
def first(self):
"""Return (but do not remove) the element at the front of the queue.
Raise Empty exception if the queue is empty.
"""
if self.is_empty():
raise EmptyError('Queue is empty')
return self._data[self._front]
def pop(self):
if self.is_empty():
raise EmptyError('Stack is empty')
item = self._top._element
self._top = self._top._next
self._size -= 1
return item
def dequeue(self):
if self.is_empty():
raise EmptyError('Stack is empty')
item = self._front._element
self._front = self._front._next
self._size -= 1
if self.is_empty():
self._back = None
return item
def dequeue(self):
if self.is_empty():
raise EmptyError('Queue is empty')
item = self._data[self._front]
self._data[self._front] = None
self._front = (self._front + 1) % self.capacity
self._size -= 1
if 0 < self._size < self.capacity // 4:
self._resize(self.capacity // 2)
return item
def dequeue(self):
if self.is_empty():
raise EmptyError('Stack is empty')
old_head = self._tail._next
if self._size == 1:
self._tail = None
else:
self._tail._next = old_head._next
self._size -= 1
return old_head._element
def delete_last(self):
if self.is_empty():
raise EmptyError('Queue is empty')
last_idx = (self._front + self._size - 1) % self.capacity
item = self._data[last_idx]
self._data[last_idx] = None
self._size -= 1
if 0 < self._size < self.capacity // 4:
self._resize(self.capacity // 2)
return item
def first(self):
if self.is_empty():
raise EmptyError('Stack is empty')
return self._front._element
def first(self):
if self.is_empty():
raise EmptyError("Deque is empty")
return self._header._next._element
def delete_last(self):
if self.is_empty():
raise EmptyError("Deque is empty")
return self._delete_node(self._trailer._prev)
def delete_first(self):
if self.is_empty():
raise EmptyError("Deque is empty")
return self._delete_node(self._header._next)
def last(self):
if self.is_empty():
raise EmptyError("Deque is empty")
return self._trailer._prev._element
def top(self):
if self.is_empty():
raise EmptyError('Stack is empty')
return self._top._element
def top(self):
if self.is_empty():
raise EmptyError('Stack is empty.')
return self._data[-1]