Transport puzzle

Transport puzzles are logistical puzzles, which represent real-life transport problems.

Description

As in shuffling puzzles, no piece is ever lost or added to the board. In contrast to shuffling puzzles, however, in transport puzzles all tokens have to follow certain routes given on the board; they cannot be lifted off the board and placed on faraway positions that have no visible connection to the from-position. Hence transport puzzles often mean that the player has to move (physical) objects in a very restricted space.

This puzzle class has several subclasses:

• sokoban puzzles
• sliding puzzles
  • with Samuel Loyd's fifteen puzzle as the most well known example
• train shunting puzzles
• river cross puzzles - see below
  

Example

A farmer has a boat, a cabbage, a goat and a wolf. He has to cross the river with his boat. His boat is small, so he can take either the cabbage, the goat or the wolf with him - but not two of them at the same time. If he leaves the goat with the cabbage unattended, the goat will eat it. Likewise, he cannot leave the goat with the wolf alone.
How many crossings must the farmer make?

Clearly the farmer first can take the goat only. After subsequently bringing one of the other two, say the cabbage, the clue is to take the goat temporarily back. He then brings the wolf and finally the goat again. Thus there are seven crossings, four forward and three back.

The famous British puzzler Henry Dudeney added several puzzles to this category.