To do so, you will take advantage of several tree stumps in the middle of the river. A tree stump provides a safe place for you to stand as you ponder your next move. To get from one stump to another, you walk along logs that connect the stumps.
In cases where no log connects to the stump you wish to reach, all is not lost. You may pick up any log adjacent to the stump on which you are standing and put it down somewhere else so that it leads to the stump you wish to reach. In order for a log to be considered adjacent to a stump, it must be oriented in the appropriate direction; for example the log in S-S is adjacent to the two stumps, but the log in S|S is not considered adjacent to the two stumps.
Each tree stump is located at a point on a square grid. Two stumps are designated as the beginning and end point of the crossing. Any two stumps lying in the same row or column of the grid may be connected by a log. At any point in time, you may perform one of the following legal moves:
- Traverse a log adjacent to the tree stump you are standing on to the tree stump at the opposite end of the log.
- Pick up a log adjacent to the tree stump you are standing on. You may not hold more than one log at a time.
- Put down the log that you are holding so that it connects the stump you are standing on to some other stump. The log must be of precisely the right length to reach the other stump. The log must rest in the water: you may not use a log to connect two stumps if there is a third stump directly between them, or if the log would cross some other log already in the water.
1 7 11 ....S...... ....|...... B---S...... ........... ........... ........... ....S.S...E