No swinging allowed: solution


For ease of reference let's label the couples 1F & 1M, 2F & 2M, and 3F & 3M, where 'F' stands for female and 'M' for male. The symbols show the state of things after each crossing, with the left side representing the destination.

Destination sideOriginal side
Initial state 1M, 1F, 2M, 2F, 3F, 3M
1) Two women cross.1F, 2F 1M, 2M, 3F, 3M
2) One of the women returns to the original side.1F1M, 2F, 2M, 3F, 3M
3) Two women cross.1F, 2F, 3F1M, 2M, 3M
4) One of the women returns to the original side.1F, 2F1M, 2M, 3F, 3M
5) The husbands of the women cross to join them.1F, 1M, 2F, 2M3F, 3M
6) A couple returns to the original side.1F, 1M2F, 2M, 3F, 3M
7) Two men cross.1F, 1M, 2M, 3M2F, 3F
8) The woman returns to the original side.1M, 2M, 3M1F, 2F, 3F
9) Two women cross.1F, 1M, 2M, 2F, 3M3F
10) One of the women returns to the original side.1F, 1M, 2M, 3M2F, 3F
11) Two women cross.1F, 2M, 2F, 2M, 3F, 3M

Note that if swinging were not a problem it would take only two crossings less to get everyone to the destination. An intriguing feature of this solution is that there are two couples on the destination side after step 5, before there is one couple at the destination, after step 6.

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