Unless they verify the source code of every library they use and verify the entire call stack; it probably has a nested for loop somewhere. Good thing computers are fast!

Depending on n, oftentimes nested loops are more readable and maintainable than the optimal solution.

Of course too many levels of nesting is inherently a code smell that indicates other issues.

Some common cases (that wouldn't be considered algorithms) are:

- working with grids (rows and columns)

- iterating over nested data structures (eg. all people in a group).

Perhaps, but “nested loops” by itself is an odd way to describe that.

that says nothing if you don't know the size of the input and the problem at hand. Sometimes the best you can do is N^2.