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Update doubly_linked_list.py #2573

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2e54707
Update doubly_linked_list.py
akashgkrishnan Oct 1, 2020
44e105f
Update doubly_linked_list.py
akashgkrishnan Oct 1, 2020
efc1a11
Update doubly_linked_list.py
akashgkrishnan Oct 1, 2020
8929b5b
Update doubly_linked_list.py
akashgkrishnan Oct 1, 2020
e934b9a
Update doubly_linked_list.py
akashgkrishnan Oct 1, 2020
69180f7
Update the doubly lnked list file
akashgkrishnan Oct 16, 2020
ad17f04
New DLL implementation
akashgkrishnan Oct 16, 2020
e5d25e4
Update doubly_linked_list.py
akashgkrishnan Oct 16, 2020
0a12a82
Update doubly_linked_list.py
akashgkrishnan Oct 16, 2020
2d947c1
Updated doubly linked list
akashgkrishnan Oct 16, 2020
f7b2e99
Update doubly_linked_list.py
akashgkrishnan Oct 16, 2020
57934ba
Rename doubly_linked_list.py to doubly_linked_list_two.py
akashgkrishnan Oct 16, 2020
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154 changes: 121 additions & 33 deletions data_structures/linked_list/doubly_linked_list.py
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Original file line number Diff line number Diff line change
Expand Up @@ -11,10 +11,10 @@


class Node:
def __init__(self, data, previous=None, next=None):
def __init__(self, data, previous=None, next_node=None):
self.data = data
self.previous = previous
self.next = next
self.next = next_node

def __str__(self):
return f"{self.data}"
Expand All @@ -33,6 +33,24 @@ def __str__(self):
current = current.next
return "<-->".join(str(node) for node in nodes)
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I find the "<—>" notation to be a lot of visual clutter. Why not just add an .__iter__() method and then return str(list(self))?

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Hi sir,
I have added in a linked list iterator class for iterating over the linked list
and removed the <--> representation.

However, I have left the str(self) same and just removed the <--> from the string as
this would keep visualizing the linked list if someone wants to visualize the data in the Linked list while debugging as opposed to the memory address that it spits out

I had previously used the <--> representation as I thought it would make the links between nodes more clear

@cclauss I have made the changes


def __contains__(self, value):
current = self.head
while current:
if current.data == value:
return True
current = current.next
return False

def get_head_data(self):
if self.head:
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Suggested change
if self.head:
return self.head.data if self.head else None

Same with get_tail_data()

return self.head.data
return None

def get_tail_data(self):
if self.tail:
return self.tail.data
return None

def set_head(self, node: Node) -> None:

if self.head is None:
Expand Down Expand Up @@ -107,6 +125,8 @@ def delete_value(self, value):
self.tail = self.tail.previous

self.remove_node_pointers(node)
else:
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The function signature does not say that this function returns a string. My sense is that we should raise an exception.

return 'Node not found'

@staticmethod
def remove_node_pointers(node: Node) -> None:
Expand All @@ -123,35 +143,103 @@ def is_empty(self):
return self.head is None


linked_list = LinkedList()
for i in range(10):
linked_list.insert(i)

print(linked_list)
# 0<-->1<-->2<-->3<-->4<-->5<-->6<-->7<-->8<-->9
print(linked_list.head)
# 0
linked_list.delete_value(0)
print(linked_list.head)
# 1
print(linked_list)
# 1<-->2<-->3<-->4<-->5<-->6<-->7<-->8<-->9
linked_list.insert_at_position(1, 100)
# 100<-->1<-->2<-->3<-->4<-->5<-->6<-->7<-->8<-->9
print(linked_list)
linked_list.delete_value(5)
print(linked_list)
# 100<-->1<-->2<-->3<-->4<-->6<-->7<-->8<-->9
print(linked_list.is_empty())
# False
linked_list.insert_at_position(12, 200)

for i in range(5):
def create_linked_list():
"""
>>> new_linked_list = LinkedList()
>>> new_linked_list.get_head_data() is None
True

>>> new_linked_list.get_tail_data() is None
True

>>> new_linked_list.is_empty()
True

>>> new_linked_list.insert(10)
>>> new_linked_list.get_head_data()
10

>>> new_linked_list.get_tail_data()
10

>>> new_linked_list.insert_at_position(position=3, value=20)
>>> new_linked_list.get_head_data()
10

>>> new_linked_list.get_tail_data()
20

>>> new_linked_list.set_head(Node(1000))
>>> new_linked_list.get_head_data()
1000

>>> new_linked_list.get_tail_data()
20

>>> new_linked_list.set_tail(Node(2000))
>>> new_linked_list.get_head_data()
1000
>>> new_linked_list.get_tail_data()
2000

>>> new_linked_list.is_empty()
False

>>> 10 in new_linked_list
True

>>> new_linked_list.delete_value(value=10)
>>> 10 in new_linked_list
False

>>> new_linked_list.delete_value(value=5000)
'Node not found'

>>> new_linked_list.delete_value(value=2000)
>>> new_linked_list.get_tail_data()
20

>>> new_linked_list.delete_value(value=1000)
>>> new_linked_list.get_tail_data()
20
>>> new_linked_list.get_head_data()
20
"""
linked_list = LinkedList()
for i in range(10):
linked_list.insert(value=i)

print(linked_list)
# 0<-->1<-->2<-->3<-->4<-->5<-->6<-->7<-->8<-->9
print(linked_list.head)
# 0
linked_list.delete_value(value=0)
print(linked_list.head)
# 1
print(linked_list)
# 1<-->2<-->3<-->4<-->5<-->6<-->7<-->8<-->9
linked_list.insert_at_position(position=1, value=100)
# 100<-->1<-->2<-->3<-->4<-->5<-->6<-->7<-->8<-->9
print(linked_list)
linked_list.delete_value(value=5)
print(linked_list)
linked_list.delete_value(linked_list.tail.data)
# for each iterations
# 100 < -->1 < -->2 < -->3 < -->4 < -->6 < -->7 < -->8 < -->9 < -->200
# 100 < -->1 < -->2 < -->3 < -->4 < -->6 < -->7 < -->8 < -->9
# 100 < -->1 < -->2 < -->3 < -->4 < -->6 < -->7 < -->8
# 100 < -->1 < -->2 < -->3 < -->4 < -->6 < -->7
# 100 < -->1 < -->2 < -->3 < -->4 < -->6
# 100<-->1<-->2<-->3<-->4<-->6<-->7<-->8<-->9
print(linked_list.is_empty())
# False
linked_list.insert_at_position(position=12, value=200)

for i in range(5):
print(linked_list)
linked_list.delete_value(linked_list.tail.data)
# for each iterations
# 100 < -->1 < -->2 < -->3 < -->4 < -->6 < -->7 < -->8 < -->9 < -->200
# 100 < -->1 < -->2 < -->3 < -->4 < -->6 < -->7 < -->8 < -->9
# 100 < -->1 < -->2 < -->3 < -->4 < -->6 < -->7 < -->8
# 100 < -->1 < -->2 < -->3 < -->4 < -->6 < -->7
# 100 < -->1 < -->2 < -->3 < -->4 < -->6


if __name__ == '__main__':
import doctest

doctest.testmod()