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Hacktoberfest: Update Linked List - print_reverse method #2792

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Merged
merged 4 commits into from
Oct 5, 2020
Merged

Hacktoberfest: Update Linked List - print_reverse method #2792

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ebf2c54
chore: update print_reverse helper method
shermanhui Oct 4, 2020
b23348a
fix: add type checking and argument typing
shermanhui Oct 5, 2020
4b1e4f8
test: add `print_reverse` test
shermanhui Oct 5, 2020
6b9748a
format code
realDuYuanChao Oct 5, 2020
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73 changes: 44 additions & 29 deletions data_structures/linked_list/print_reverse.py
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Original file line number Diff line number Diff line change
@@ -1,4 +1,4 @@
# Program to print the elements of a linked list in reverse
from typing import List


class Node:
Expand All @@ -8,48 +8,63 @@ def __init__(self, data=None):

def __repr__(self):
"""Returns a visual representation of the node and all its following nodes."""
string_rep = ""
string_rep = []
temp = self
while temp:
string_rep += f"<{temp.data}> ---> "
string_rep.append(f"{temp.data}")
temp = temp.next
string_rep += "<END>"
return string_rep
return "->".join(string_rep)


def make_linked_list(elements_list):
def make_linked_list(elements_list: List):
"""Creates a Linked List from the elements of the given sequence
(list/tuple) and returns the head of the Linked List."""

# if elements_list is empty
(list/tuple) and returns the head of the Linked List.
>>> make_linked_list([])
Traceback (most recent call last):
...
Exception: The Elements List is empty
>>> make_linked_list([7])
7
>>> make_linked_list(['abc'])
abc
>>> make_linked_list([7, 25])
7->25
"""
if not elements_list:
raise Exception("The Elements List is empty")

# Set first element as Head
head = Node(elements_list[0])
current = head
# Loop through elements from position 1
for data in elements_list[1:]:
current.next = Node(data)
current = head = Node(elements_list[0])
for i in range(1, len(elements_list)):
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@shellhub Thanks for the review and merge, I was hoping to improve the algorithm by using the generator as a part of my Hacktoberfest contribution for #2510. What was the reason for removing it for the regular iteration over a list?

i.e. (what I had before)

for data in (elements_list[i] for i in range(1, list_length)):

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This way need to generate a list and then iterate. It's slow.

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@realDuYuanChao realDuYuanChao Oct 5, 2020 •
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def fun1() -> None:
    my_list = []
    elements_list = [14, 52, 14, 12, 43]
    for i in range(0, len(elements_list)):
        my_list.append(i)


def fun2() -> None:
    my_list = []
    elements_list = [14, 52, 14, 12, 43]
    for data in (elements_list[i] for i in range(0, len(elements_list))):
        my_list.append(data)


if __name__ == '__main__':
    import timeit

    print(timeit.timeit("fun1()", setup="from __main__ import fun1", number=100000))
    print(timeit.timeit("fun2()", setup="from __main__ import fun2", number=100000))

output:
0.087008857
0.119698832

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@shermanhui shermanhui Oct 5, 2020 •
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Thanks, good catch, @shellhub. That was informative! I only ran timeit against the list slicing. I should have checked the regular iteration as well. I guess it's also better to keep it simple! 😃

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How we Iris dataset from an online source. Read the dataset into a data structure, preferably
in a 2D array??? Anyone help me please its my assignment

current.next = Node(elements_list[i])
current = current.next
return head


def print_reverse(head_node):
"""Prints the elements of the given Linked List in reverse order"""

# If reached end of the List
if head_node is None:
return None
else:
# Recurse
def print_reverse(head_node: Node) -> None:
"""Prints the elements of the given Linked List in reverse order
>>> print_reverse([])
>>> linked_list = make_linked_list([69, 88, 73])
>>> print_reverse(linked_list)
73
88
69
"""
if head_node is not None and isinstance(head_node, Node):
print_reverse(head_node.next)
print(head_node.data)


list_data = [14, 52, 14, 12, 43]
linked_list = make_linked_list(list_data)
print("Linked List:")
print(linked_list)
print("Elements in Reverse:")
print_reverse(linked_list)
def main():
from doctest import testmod

testmod()

linked_list = make_linked_list([14, 52, 14, 12, 43])
print("Linked List:")
print(linked_list)
print("Elements in Reverse:")
print_reverse(linked_list)


if __name__ == "__main__":
main()