Once you "memorize" a core set of data structures and algorithms, you can apply them to a variety of "novel" problems. The issue is those technique that are memorized, that become useful in solving these problems, aren't intuitive, despite their deceptive simplicity. In reality there's little memorization of solutions, and much memorization of useful techniques (data structures, algorithmic techniques) that are useful for these problems. And the more you do, the more you'll have at your disposal for "novel" problems. Further, many of these memorized techniques are not as intuitive as they seem. Quite a few resulted in publications when they were discovered.
5 years ago the fast/slow pointer technique for cycle detection could have been impossibly hard, now I see questions that just assume the candidate knows this. Every year the bar gets higher.
