A) is completely possible in a few minutes if you have a prewritten permutation function.

for C) I wrote about 30 lines in python - 20 of them file handling - to solve the problem (after a few hours of deliberation). What matters is your speed in figuring out how to write a proper algorithm. The codewriting will not take near as much time.

B) is the one where they surprised me the most. It took me about 150 lines to finish off that beast in about 3 hours, and there are definitely errors in the large output even still. I would love to see how they did it.