Is Quizlet's “Learn” algorithm the same as Anki's spaced repetition? If not, how does it differ?
You might like to have a look at this article on Quizlet and it's algorithm(s), and both the Anki manual and the Wikipedia article on Anki to learn about the algorithms that are used in it. You will see from the Anki manual and the Wikipedia article that the Anki algorithm derives from the algorithm originally introduced for SuperMemo, although the two now differ substantially.
The article on Quizlet explains that it works in a similar way to Anki. However, the details of the algorithm are not clearly stated so it is impossible to compare the two directly. In addition, the Anki algorithm has changed over time as, no doubt, has the Quizlet algorithm.
One last thing. There are add-ons for Anki that change the algorithm entirely; a newly released addon does away with the "ease" parameter entirely and relies instead on an approach driven by Bayesian statistics.