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Optimize sieveOfEratosthenes: reduced memory usage and iterations#1813

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Sumit210106
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  • Mark only odd multiples starting from i² to reduce iterations
  • Collect primes after marking to avoid duplicates and simplify logic
  • Explicitly include 2 and skip even numbers throughout

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Describe your change:

  • Optimize an existing algorithm (sieveOfEratosthenes)

Checklist:

  • I have readCONTRIBUTING.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 (sieveOfEratosthenes.js).
  • All filenames follow UpperCamelCase (PascalCase) style.
  • The algorithm has a URL in its comments pointing to Wikipedia.
  • (Optional) If this PR fixes an open issue, I have addedFixes: #ISSUE_NO in the commit message.

Summary of Improvements

  • Reduced memory usage by ~50% by skipping even numbers (except 2).
  • Reduced number of iterations:
    • Outer loop increments by 2 (odd-only).
    • Inner loop starts fromi*i and marks only odd multiples (j += 2*i).
  • Same time complexityO(n log log n) but with a smaller constant factor → faster in practice.
  • Added clearer inline comments in the code for maintainability.

Example

sieveOfEratosthenes(20)// Output: [2, 3, 5, 7, 11, 13, 17, 19]

- Mark only odd multiples starting from i² to reduce iterations- Collect primes after marking to avoid duplicates and simplify logic- Explicitly include 2 and skip even numbers throughout
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codecov-commenter commentedOct 1, 2025
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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.92%. Comparing base (08d8c6b) to head (33af5aa).

Additional details and impacted files
@@           Coverage Diff           @@##           master    #1813   +/-   ##=======================================  Coverage   85.91%   85.92%           =======================================  Files         379      379             Lines       19778    19789   +11       Branches     3015     3022    +7     =======================================+ Hits        16993    17004   +11  Misses       2785     2785

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@raklaptudirmraklaptudirmAwaiting requested review from raklaptudirmraklaptudirm is a code owner

@appgurueuappgurueuAwaiting requested review from appgurueuappgurueu is a code owner

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