Puzzle time - Medieval etiquette and rivers
-
wrote on 16 Feb 2021, 08:59 last edited by
In eighth century Europe, it was considered unseemly for a man to be in the presence of a married woman, unless her husband was there as well. This posed problems for three married couples who wished to cross a river, the only means being a rowboat that could carry at most two people.
Can they get to the other side without violating their social norms? If so, what's the minimum number of crossings needed?
-
wrote on 16 Feb 2021, 10:42 last edited by
(insert Mike Pence joke here)
-
wrote on 16 Feb 2021, 10:46 last edited by
Sounds similar to the wolf/goat/cabbage puzzle.
-
wrote on 16 Feb 2021, 12:22 last edited by Klaus
:::
Let's designate the people M 0,W 0,M 1,W 1,M 2,W 2, whereby M x is married to W x.Here's a valid move sequence.
[M 0,W 0],[M 0],[W 1,W 2],[W 1],[M 2,M 0],[W 0,M 0],[M 1,M 0],[W 2],[W 1,W 0],[M 2],[W 2,M 2]
From what I can see, there are 192 different solutions. If you factor out permutations, 32 distinct solutions remain, 8 of which have length 11, 8 of which have length 13, and 16 of which have length 15. So, the minimum number of crossings is 11.
Would be a nice exercise to model and verify this in a class on verification of finite state systems. It would be easy to express the safety condition and the desired final state in LTL.
::: -
wrote on 16 Feb 2021, 12:24 last edited by brenda
:::
W1 makes 2 trips to ferry W2 and W3 across.
W1 ferries H1 across, and W2W3 return.
H2 ferries H3 across.
H2 ferries W2 across. H3 returns.
H3 ferries W3 across.
::: -
wrote on 23 Feb 2021, 21:50 last edited by
So, what's the "official" solution?
-
wrote on 23 Feb 2021, 23:42 last edited by
It is 11 under the ‘hard constraint’ where you can’t violate the taboos even in the moments of switching in and out of boats.
Under the ‘soft constraint’, where you only prevent taboo-violations on the shores and in the boat itself you can do 9.
-
wrote on 24 Feb 2021, 14:22 last edited by
Which reminds me of an important PSA. Don’t ever try to fuck in a canoe.