The brainbuster

Find the solution to this brainbuster and win £200 of Amazon vouchers to spend on high-tech!

A division of Acme Software has five engineers, each in their own office. Which is just as well, because none of the engineers can stand to be in the same office at the same time as another one.

See the diagram below - we’ve shortened the names to single letters to protect the engineers’ identities (although I’m sure you could name names). There’s one empty office.

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Now B and E need to swap offices - what is the minimum number of moves that will achieve this? (By the way, the others aren’t bothered about which office they work in.)

You’ll need to give a valid solution showing which engineer moves into the empty office each time. For example, ACD…

Show your workings. Only complete entry forms will be considered. The judge's decision is final.

The competition closes on Sunday 17th December 2017.