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Fix shuffle algorithm for friends page #1222
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Implement Fisher-Yates shuffle [1] to ensure that each random permutation is equally likely to be produced. The algorithm "repeatedly pick two random indices i and j between 0 and N-1 and swap element i and j" is a simple, straightforward algorithm, but unfortunately it tends to produce some random orderings more frequently than others. There is an equally simple algorithm by Fischer and Yates that does not have the same problem: "for i = 0 to N-1, pick a random index j between 0 and i and swap element i and j". [1]: https://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle
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Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @ashleygwilliams (or someone else) soon. If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes. Please see the contribution instructions for more information. |
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Implement Fisher-Yates shuffle to ensure that each random permutation is equally likely to be produced.
The algorithm "repeatedly pick two random indices i and j between 0 and N-1 and swap element i and j" is a simple, straightforward algorithm, but unfortunately it tends to produce some random orderings more frequently than others. There is an equally simple algorithm by Fischer and Yates that does not have the same problem: "for i = 0 to N-1, pick a random index j between 0 and i and swap element i and j".