[musicale]

Missing the instruction panel where the customer is attempting to follow the baffling instructions and has to use a wired phone to call the store for help.

Getting quicksort's boundary conditions right (avoiding off-by-one errors, infinite recursion, etc.) can be tricky.

Another popular algorithm that can be hard to get right is binary search.

[JdeBP]

BINÄRY SEARCH has you covered. (-:

* https://idea-instructions.com/binary-search/

[mvhv]

The second page is borderline incomprehensible, I'm not sure I would ever understand what it's trying to say if I didn't already know.

[jalk]

Stuck in second round of step 2, since there is no middle cup to lift!