列表迭代器
"""
File: linkedlistiterator.py
Author: Zhu nw
"""
from node import TwoWayNode
class LinkedListIterator(object):
"""Represents the list iterator for an linked list."""
def __init__(self, backingStore):
self._backingStore = backingStore
self._modCount = backingStore.getModCount()
self.first()
def first(self):
"""Returns the cursor to the beginning of the backing store."""
self._cursor = self._backingStore._head.next
self._lastItemPos = self._backingStore._head
def hasNext(self):
"""Returns True if the iterator has a next item or False otherwise."""
return not self._cursor is self._backingStore._head
def next(self):
"""Preconditions: hasNext returns True
The list has not been modified except by this iterator's mutators.
Returns the current item and advances the cursor to the next item.
Postcondition: lastItemPos is now defined.
Raises: ValueError if no next item.
AttributeError if illegal mutation of backing store."""
if not self.hasNext():
raise ValueError("No next item in list iterator")
if self._modCount != self._backingStore.getModCount():
raise AttributeError("Illegal modification of backing store")
self._lastItemPos = self._cursor
self._cursor = self._cursor.next
return self._lastItemPos.data
def last(self):
"""Moves the cursor to the end of the backing store."""
self._cursor = self._backingStore._head.previous
self._lastItemPos = self._backingStore._head
def hasPrevious(self):
"""Returns True if the iterator has a previous item or False otherwise."""
return not self._cursor is self._backingStore._head
def previous(self):
"""Preconditions: hasPrevious returns True
The list has not been modified except by this iterator's mutators.
Returns the current item and moves the cursor to the previous item.
Postcondition: lastItemPos is now defined.
Raises: ValueError if no next item.
AttributeError if illegal mutation of backing store."""
if not self.hasPrevious():
raise ValueError("No previous item in list iterator")
if self._modCount != self._backingStore.getModCount():
raise AttributeError("Illegal modification of backing store")
self._lastItemPos = self._cursor
self._cursor = self._cursor.previous
return self._lastItemPos.data
def replace(self, item):
"""Preconditions: the current position is defined.
The list has not been modified except by this iterator's mutators.
Replaces the items at the current position with item.
Raises: AttibuteError if position is not defined.
AttributeError if illegal mutation of backing store."""
if self._lastItemPos is self._backingStore._head:
raise AttributeError("The current position is undefined.")
if self._modCount != self._backingStore.getModCount():
raise AttributeError("List has been modified illegally.")
self._lastItemPos.data = item
self._lastItemPos = self._backingStore._head
def insert(self, item):
"""Preconditions:
The list has not been modified except by this iterator's mutators.
Adds item to the end if the current position is undefined, or
inserts it at that position.
Raises: AttributeError if illegal mutation of backing store."""
if self._modCount != self._backingStore.getModCount():
raise AttributeError("List has been modified illegally.")
if self._lastItemPos is self._backingStore._head:
#self._backingStore.add(item)
newNode = TwoWayNode(item, self._lastItemPos.previous, self._lastItemPos)
self._lastItemPos.previous.next = newNode
self._lastItemPos.previous = newNode
self._backingStore.incModCount()
self._backingStore.incSize()
else:
#self._backingStore.insert(self._lastItemPos, item)
#self._lastItemPos = -1
newNode = TwoWayNode(item, self._lastItemPos.previous, self._lastItemPos)
self._lastItemPos.previous.next = newNode
self._lastItemPos.previous = newNode
self._backingStore.incModCount()
self._backingStore.incSize()
self._lastItemPos = self._backingStore._head
self._modCount += 1
def remove(self):
"""Preconditions: the current position is defined.
The list has not been modified except by this iterator's mutators.
Pops the item at the current position.
Raises: AttibuteError if position is not defined.
AttributeError if illegal mutation of backing store."""
if self._lastItemPos is self._backingStore._head:
raise AttributeError("The current position is undefined.")
if self._modCount != self._backingStore.getModCount():
raise AttributeError("List has been modified illegally.")
#item = self._backingStore.pop(self._lastItemPos)
#item = self._lastItemPos
self._lastItemPos.previous.next = self._lastItemPos.next
self._lastItemPos.next.previous = self._lastItemPos.previous
# If the item removed was obtained via next, move cursor back
#if self._lastItemPos < self._cursor:
# self._cursor -= 1
self._modCount += 1
self._backingStore.incModCount()
self._backingStore.decSize()
self._lastItemPos = self._backingStore._head测试代码
"""
File: testlistiterator.py
A tester program for list iterator implementation.
"""
from arraylist import ArrayList
from linkedlist import LinkedList
#from arraysortedlist import ArraySortedList
def test(listType):
"""Expects a list type as an argument and runs some tests
on objects of that type."""
print("Create a list with 1-9")
lyst = listType(range(1, 10))
print("Length:", len(lyst))
print("Items (first to last):", lyst)
# Create and use a list iterator
listIterator = lyst.listIterator()
print("Forward traversal: ", end="")
listIterator.first()
while listIterator.hasNext():
print(listIterator.next(), end = " ")
print("\nBackward traversal: ", end="")
listIterator.last()
while listIterator.hasPrevious():
print(listIterator.previous(), end=" ")
print("\nInserting 10 before 3: ", end="")
listIterator.first()
for count in range(3):
listIterator.next()
listIterator.insert(10)
print(lyst)
print("Removing 2: ", end="")
listIterator.first()
for count in range(2):
listIterator.next()
listIterator.remove()
print(lyst)
print("Removing all items")
listIterator.first()
while listIterator.hasNext():
listIterator.next()
listIterator.remove()
print("Length:", len(lyst))
test(ArrayList)
print("\n\n")
test(LinkedList)测试结果
Create a list with 1-9
Length: 9
Items (first to last): [1, 2, 3, 4, 5, 6, 7, 8, 9]
Forward traversal: 1 2 3 4 5 6 7 8 9
Backward traversal: 9 8 7 6 5 4 3 2 1
Inserting 10 before 3: [1, 2, 10, 3, 4, 5, 6, 7, 8, 9]
Removing 2: [1, 10, 3, 4, 5, 6, 7, 8, 9]
Removing all items
Length: 0
Create a list with 1-9
Length: 9
Items (first to last): [1, 2, 3, 4, 5, 6, 7, 8, 9]
Forward traversal: 1 2 3 4 5 6 7 8 9
Backward traversal: 9 8 7 6 5 4 3 2 1
Inserting 10 before 3: [1, 2, 10, 3, 4, 5, 6, 7, 8, 9]
Removing 2: [1, 10, 3, 4, 5, 6, 7, 8, 9]
Removing all items
Length: 0