Alexander Shapovalov Crosses a River
Alexander Shapovalov is a prolific puzzle writer. He has a special webpage of his river-crossing puzzles (in Russian). Here is one of these puzzles.
Three swindlers have two suitcases each. They approach a river they wish to cross. There is one boat that can carry three objects, where a person or a suitcase counts as one object. No swindler can trust his suitcase to his swindler friends when he is away, but each swindler doesn’t mind his suitcases left alone at the river shore. Can they cross the river?
Two of them approach the river from one shore, and the third – from the other?7 September 2016, 8:31 pm
The puzzle assumes that they approach from the same shore.7 September 2016, 8:52 pm
I think I have a solution7 September 2016, 9:30 pm
Swindler A takes his across and leaves them there. He then returns alone (no suitcases) to the near side. Next all 3 cross together and B and C return. Leaving A on the far side with his suitcases and B and C on the near side with the boat and their cases. B then takes the boat and his two cases across. Leaving A, B and there stuff on the far side with the boat and C on the near with his cases. A and B return together and fetch C. C then takes the boat back alone to collect his stuff.8 September 2016, 2:14 am
Can a boat with no people cross the river?8 September 2016, 2:49 am
I have a solution, in seven crossings.8 September 2016, 9:40 am
Haha, the math world is so small! I remember going to Alexanders math circle in Stockholm to do problem solving.2 October 2016, 11:53 am
At least some of Shapovalov’s puzzles are now also available in English: https://ashap.info/Zadachi/eng/River.html5 October 2016, 9:11 am
Yes, they (the swindlers) can cross the river! They all simply get into the boat and go across together in one trip.17 October 2016, 2:25 pm
The puzzle does not state that their cases have to go with them. It specifically says that “each swindler doesn’t mind his suitcases left alone at the river shore”.
Jonathan Kariv’s answer is correct6 December 2016, 7:22 am