class _DoubleLinkedbase:
class _Node:
__slots__ = "_element", "_next", "_prev"
def __init__(self, element, next, prev):
self._element = element
self._next = next
self._prev = prev
def __init__(self):
self._header = self._Node(None, None, None)
self._tailer = self._Node(None, None, None)
self._size = 0
self._header._next = self._tailer
self._tailer._prev = self._header
def __len__(self):
return self._size
def is_empty(self):
return self._size == 0
def _insert_between(self, e, predecessor, successor):
newest = self._Node(e, predecessor, successor)
predecessor._next = newest
successor._prev = newest
self._size += 1
return newest
def _delete_node(self, node):
predecessor = node._prev
successor = node._next
predecessor._next = successor
successor._prev = predecessor
self._size -= 1
element = node._element
node._prev = node._next = node._element = None
return element
class PositionList(_DoubleLinkedbase):
class Position:
"""an abstraction representing the location of a single element"""
def __init__(self, container, node):
self._container = container # container是用來干嘛的?
self._node = node
def element(self):
return self._node._element
def __eq__(self, other):
return type(other) is type(self) and other._node is self._node
def __ne__(self, other):
return not (self == other)
def _validate(self, p):
if not isinstance(p, self.Position):
raise TypeError("p must be proper Position type")
if p._container is not self:
raise ValueError("p does not belong to this container")
if p._node._next is None:
raise ValueError("p is no longer valid")
return p._node
def _make_position(self, node):
if node is self._header or node is self._tailer:
return None
else:
return self.Position(self, node) # 只有一個形參node？？
def first(self):
return self._make_position(self._header._next)
def last(self):
return self._make_position(self._tailer._prev)
def before(self, p):
node = self._validate(p)
return self._make_position(node._prev)
def after(self, p):
node = self._validate(p)
return self._make_position(node._next)
def __iter__(self):
cursor = self.first()
while cursor is not None:
yield cursor.element()
cursor = self.after(cursor)
def _insert_between(self, e, prenode, sucnode):
node = super()._insert_between(e, prenode, sucnode)
return self._make_position(node)
def addfirst(self, e):
return self._insert_between(e, self._header, self._header._next)
def addlast(self, e):
return self._insert_between(e, self._tailer._prev, self._tailer)
def addbefore(self, p, e):
original = self._validate(p)
return self._insert_between(e, original._prev, original)
def addafter(self, p, e):
original = self._validate(p)
return self._insert_between(e, original, original._next)
def delete(self, p):
original = self._validate(p)
return self._delete_node(original)
def replace(self, p, e):
original = self._validate(p)
t = original._element
original_element = e
return t
-------------------------------
上面為書中對positional list 的定義，不太懂Position class是如何獲取值對應的位置的，Position里面的container起什么作用啊？
請大佬幫忙解釋一下，最好能給一段測驗代碼，謝謝！！
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標籤：數據結構與算法
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