96c06b44bd
- implement the __len__() and __iter__() methods - the __len__() method has a bug in that it will incorrectly calculate the length of a linked-list if `pop` or `shift` are called on an empty linked-list. Fortunately the README states that: > pop or shift will never be called on an empty list.
62 lines
1.6 KiB
Python
62 lines
1.6 KiB
Python
class Node(object):
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def __init__(self, value, next=None, prev=None):
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self.value = value
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self.next = next
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self.prev = prev
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class LinkedList(object):
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def __init__(self):
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self.head = None
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self.tail = None
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self.length = 0
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def push(self, value):
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new_node = Node(value)
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if not self.head:
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self.head = self.tail = new_node
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else:
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new_node.prev = self.tail
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self.tail.next = new_node
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self.tail = new_node
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self.length += 1
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def pop(self):
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node = self.tail
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if node is None or node.prev is None:
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self.head = self.tail = None
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else:
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self.tail = self.tail.prev
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self.tail.next = None
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self.length -= 1
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return node.value
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def shift(self):
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node = self.head
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if node is None or node.next is None:
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self.head = self.tail = None
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else:
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self.head = self.head.next
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self.head.prev = None
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self.length -= 1
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return node.value
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def unshift(self, value):
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new_node = Node(value)
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if not self.head:
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self.head = self.tail = new_node
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else:
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new_node.next = self.head
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self.head.prev = new_node
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self.head = new_node
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self.length += 1
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def __len__(self):
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return self.length
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def __iter__(self):
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current_node = self.head
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while (current_node):
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yield current_node.value
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current_node = current_node.next
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