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[Searches] Fix Binary Search bug with duplicate elements#13946

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poyea merged 6 commits intoTheAlgorithms:masterfrom
shuhao-alan-fan:fix-merge-sort-empty-list-issue#13901
Dec 13, 2025
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[Searches] Fix Binary Search bug with duplicate elements#13946
poyea merged 6 commits intoTheAlgorithms:masterfrom
shuhao-alan-fan:fix-merge-sort-empty-list-issue#13901

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@shuhao-alan-fan shuhao-alan-fan commented Nov 22, 2025 •
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Describe your change:

This PR fixes a bug where the Binary Search algorithm returned incorrect results (or failed) when the input list contained duplicate elements.

I have updated the logic to handle duplicates correctly and added doctests to verify the fix.

Fixes #13886

  • Add an algorithm?
  • Fix a bug or typo 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 Binary Search gives wrong output for duplicate elements #13886".

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shuhao-alan-fan commented Nov 22, 2025

Hi maintainers, this PR fixes issue #13886 and all tests + pre-commit checks are passing.
Whenever you have time, I would appreciate a review.

Thank you!

@shuhao-alan-fan shuhao-alan-fan changed the title Fixes #13886 [Searches] Fix Binary Search bug with duplicate elements Dec 12, 2025
@poyea poyea requested a review from Copilot December 12, 2025 16:54
@poyea poyea force-pushed the fix-merge-sort-empty-list-issue#13901 branch from 37fe148 to ad1574f Compare December 12, 2025 16:54
Copilot AI reviewed Dec 12, 2025
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Pull request overview

This PR adds a new binary_search_with_duplicates function to handle binary search in sorted lists containing duplicate elements. The implementation uses lower_bound and upper_bound helper functions to find the range of all occurrences of the target value, addressing issue #13886.

Key changes:

  • Adds binary_search_with_duplicates function that returns a list of all indices where the target occurs
  • Implements lower_bound and upper_bound as nested helper functions using binary search
  • Includes doctests covering single occurrences, multiple duplicates, and not-found cases

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shuhao-alan-fan and others added 2 commits December 12, 2025 17:38
@shuhao-alan-fan
Add docstrings to binary search functions
8af1e5b 
Added docstrings for lower_bound and upper_bound functions.
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Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated 6 comments.

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@shuhao-alan-fan
Update searches/binary_search.py
58ad165 
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
@algorithms-keeper algorithms-keeper bot added the awaiting reviews This PR is ready to be reviewed label Dec 13, 2025
@shuhao-alan-fan
Refactor docstrings for lower_bound and upper_bound
f16b1d2 
Updated docstring parameter and return type annotations for lower_bound and upper_bound functions.
@algorithms-keeper algorithms-keeper bot removed the awaiting reviews This PR is ready to be reviewed label Dec 13, 2025
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Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated 3 comments.

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@poyea
Update searches/binary_search.py
2d4dfe1 
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
@algorithms-keeper algorithms-keeper bot added the awaiting reviews This PR is ready to be reviewed label Dec 13, 2025
@poyea poyea merged commit 2c15b8c into TheAlgorithms:master Dec 13, 2025
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@algorithms-keeper algorithms-keeper bot removed the awaiting reviews This PR is ready to be reviewed label Dec 13, 2025
thotaDeepika added a commit to thotaDeepika/Python that referenced this pull request Dec 16, 2025
@thotaDeepika
Merge pull request #1 from TheAlgorithms/master
46165bb 
[Searches] Fix Binary Search bug with duplicate elements (TheAlgorithms#13946)
@thotaDeepika thotaDeepika mentioned this pull request Dec 16, 2025
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Binary Search gives wrong output for duplicate elements

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