Four areas of land are linked to each other by seven bridges as shown.
Is it possible to cross over all these bridges without crossing over the same one more than once? Try it!
Click on any white circle. This is your starting point.
Click on another white circle to move across land or across a bridge. As you cross a bridge, it disappears — you cannot cross it again! Your challenge is to cross each bridge.
Can you do it?
The impossibility of this challenge was proved over 200 years ago by a mathematician named Euler. He proved mathematically that if you have a four point network (each area of land is a point to which you can walk) with an odd number of ways to get to each point (there are seven bridges), it cannot be done!
This is an example of network theory, a branch of mathematics used in the design of complex networks such as those in telephone exchanges and electrical circuits.
Make your own network puzzles. What would happen if you have a five point network with an odd number of links? Or a four point network with an even number of links? Try it and find out.