For each job, say whether a loop or recursion is the better choice, and why…

Plan. Recursion is clearer for a problem that is made of smaller copies of itself. A loop is better for a simple repeat, and when the depth would be large.

1. A loop (or the formula). A simple repeat, and a depth of 1000 is at the limit of recursion.
2. Recursion. The depth is not known, and each folder is a smaller copy of the problem.
3. A loop. A simple repeat. (A recursive countdown also works for 10 items, but it gives no gain.)
4. A loop (or recursion with a memory). The simple recursion is far too slow for 40.
5. A loop (or len). Recursion would be too deep for a long text.