Henry Ernest Dudeney/Modern Puzzles/158 - The Nine Bridges

by : $158$

 * The Nine Bridges
 * The diagram represents the map of a district with a peculiar system of irrigation.
 * The lines are waterways enclosing the four islands $A$, $B$, $C$, and $D$, each with its house,
 * and it will be seen that there are nine bridges available.


 * Dudeney-Modern-Puzzles-158.png


 * Whenever Tompkins leaves his house to visit his friend Johnson, who lives in one of the others,
 * he always carries out the eccentric rule of crossing every one of the bridges once, and once only,
 * before arriving at his destination.
 * How many different routes has he to select from?
 * You may choose any house you like as the residence of Tompkins.