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104 lines
2.2 KiB
Python
104 lines
2.2 KiB
Python
"""
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Implementation of Linked Lists
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@jlengrand
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2013/12
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"""
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class SingleListItem():
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"""
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Item from a Single Linked List.
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Contains only a previous next element, and a value
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"""
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def __init__(self, value, nexti=None):
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self.value = value
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self.nexti = nexti # pointer of the next element in the list
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def has_next(self):
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"""
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Returns True if the item has a next value
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"""
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return not (self.nexti is None)
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class SingleLinkedList():
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"""
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Linked list with only one link between items.
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The list can only be traversed one way"""
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def __init__(self):
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self._size = 0
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self._root = None # reference of the head
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def add(self, value):
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"""
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Adds a new element to the end of the list
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"""
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if self._root is None:
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# empty tree
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self._root = SingleListItem(value)
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else:
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curr = self._root
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while(curr.nexti is not None):
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#gets last item
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curr = curr.nexti
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item = SingleListItem(value)
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curr.nexti = item
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self._size += 1
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def delete_item(self, node=None):
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"""
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Deletes the nth node of the list. (0 being the first element)
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If node is None, deletes the first element of the list.
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"""
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if node == None:
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item = self._root.nexti
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self._root = item
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self._size -= 1
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elif node >= self._size:
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raise Exception("Requested value out of list bounds")
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else:
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# Find the element before
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# Find the element after
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# Link the element after to the element before
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# Reduce the size
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# I want to traverse the list only once
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item = self._root
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for i in range(node - 1):
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item = item.nexti
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item_bef = item
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item_af = item.nexti.nexti
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item_bef.nexti = item_af
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self._size -= 1
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def __len__(self):
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# Returns the number of elements in the list
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return self._size
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def __str__(self):
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"""
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Prints out all values in the list
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This way of doing is not exactly clever, given the fact that I put
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everything in memory before printing
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"""
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to_print = ""
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curr = self._root
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to_print += str(curr.value)
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while(curr.nexti is not None):
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curr = curr.nexti
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to_print += ", " + str(curr.value)
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return to_print
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if __name__ == "__main__":
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ll = SingleLinkedList()
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ll.add(3)
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ll.add(4)
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ll.add(5)
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ll.add(6)
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print ll
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