The puzzle being so simple, one might ask: Can we change it to make it more complicated? What happens if we are traveling with a group of children and have to cross a river with a boat. Some pairs of children, however, can not be left alone, since they would immediately start fighting.
In our concrete example we have 5 children with names 1, 2, 3, 4, and 5. Child 1 would start fighting with any of the children 2, 3, 4, but not with child 5, since she is very philosophical. But child 5 would start battling with child 4 immediately. The tension between the children, the conflicts, are visualized below with red lines.
Click the refresh button if you don't see numbers from 1 to 5 on the left.
It is quite obvious that a small boat, holding only one child, will not suffice. If we board child 1, then there the conflict between children 4 and 5 remains on the bank, but child 1 can also not be left behind. So let's take a boat that can take two children, together with you, the rower (not visible in the applet). How often do you have to cross the river to carry all children from the left bank to the right bank?