Meeting Table

Let there be three groups of people waiting to attend a meeting. There are $\textbf N$ people in each group. There is a round table in the meeting room. The coordinator wants them to sit in a way around the table that there will be no two-person of the same group sitting adjacently. He decides to make such an arrangement step by step.


This is a companion discussion topic for the original entry at https://toph.co/p/hey-you-don-t-help-them-to-bury-the-light