IBM Ponder This #221 · September 2016

It is impossible to seat three people (Alice, Bob, and Charlie) in three places for six hours, while changing places each hour in such a way that each hour has a different seating permutation and no one stays in his or her chair during two consecutive hours. Here is an "almost" solution:

A B C A B C
B C A C A B
C A B B C A

The only violation is the "B B" in the middle of the third line.

Our challenge for this month is to design a seating plan for four people for 24 hours in such a way that they don't repeat the same seating arrangement, and the number of violations is minimal, where violations refer to the same person sitting in the same place he sat in during one of the two preceding hours.

Solution

Best opened after a real attempt

To be added.