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Remove extra len calls in doubly-linked-list's methods #8600

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merged 1 commit into from
Apr 1, 2023

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amirsoroush
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Describe your change:

I reduced the number of calls to __len__ by storing the result into a local variable as it's currently a costly method( O(N) ).

To elaborate more: Suppose we insert an item at the tail like:

l = DoublyLinkedList()
l.insert_at_tail("foo")
l.insert_at_tail("boo")   # <------- Here

The second call to insert_at_tail causes __len__ to be called three times:

  1. inside self.insert_at_nth(len(self), data) (because of delegating to insert_at_nth)
  2. one at if not 0 <= index <= len(self) inside insert_at_nth
  3. one at elif index == len(self) inside insert_at_nth

Same thing happens in delete_at_nth.


  • Add an algorithm?
  • Fix a bug or typo in an existing algorithm?
  • Documentation change?

Checklist:

  • I have read CONTRIBUTING.md.
  • This pull request is all my own work -- I have not plagiarized.
  • I know that pull requests will not be merged if they fail the automated tests.
  • This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
  • All new Python files are placed inside an existing directory.
  • All filenames are in all lowercase characters with no spaces or dashes.
  • All functions and variable names follow Python naming conventions.
  • All function parameters and return values are annotated with Python type hints.
  • All functions have doctests that pass the automated testing.
  • All new algorithms include at least one URL that points to Wikipedia or another similar explanation.
  • If this pull request resolves one or more open issues then the commit message contains Fixes: #{$ISSUE_NO}.

@algorithms-keeper algorithms-keeper bot added awaiting reviews This PR is ready to be reviewed enhancement This PR modified some existing files labels Apr 1, 2023
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@dhruvmanila dhruvmanila left a comment

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Makes sense, thanks!

@algorithms-keeper algorithms-keeper bot removed the awaiting reviews This PR is ready to be reviewed label Apr 1, 2023
@dhruvmanila dhruvmanila changed the title remove extra length check in doubly-linked-list's methods Remove extra len calls in doubly-linked-list's methods Apr 1, 2023
@dhruvmanila dhruvmanila merged commit 6371088 into TheAlgorithms:master Apr 1, 2023
tianyizheng02 pushed a commit to tianyizheng02/Python that referenced this pull request May 29, 2023
sedatguzelsemme pushed a commit to sedatguzelsemme/Python that referenced this pull request Sep 15, 2024
@isidroas isidroas mentioned this pull request Jan 25, 2025
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2 participants