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Update longest_increasing_subsequence.py #12499

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squenson1
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Counter-example that doesn't return the longest increasing subsequence

Describe your change:

The algorithm longest_increasing_subsequence.py has a bug for the sequence [28, 26, 12, 23, 35, 39] as it returns [26, 35, 39] instead of [12, 23, 35, 39]. (No change in code has been done).

  • Add an algorithm?
  • Fix a bug or typo in an existing algorithm?
  • Indicate a bug in an existing algorithm?
  • Add or change doctests? -- Note: Please avoid changing both code and tests in a single pull request.
  • 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 description above includes the issue number(s) with a closing keyword: "Fixes #ISSUE-NUMBER".

Counter-example that doesn't return the longest increasing subsequence
@MaximSmolskiy
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@squenson1 Thanks for counter-example.

In future, please create issues for such problems (as I created #12510) - not pull requests.

Additionally, I found a problem in current doctest

>>> longest_subsequence([9, 8, 7, 6, 5, 7])
[8]

Correct answers could be [7, 7], [6, 7] or [5, 7]

I am closing this pull request - feel free to fix current incorrect implementation and create corresponding pull request.

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2 participants