How to work out if the network is traversable

The Konigsberg Bridge Problem 

The seven bridges of Konigsberg is a historical mathematic problem. It's negative resolution by world-famous mathematician Leonhard Euler in 1736 laid the foundation for graph theory. 

The problem was that could you travel across all seven bridges of Konigsberg without going through the same bridge twice.

Leonhard Euler 

Leonhard Euler was a Swiss mathematician, physicist, astronomer, geographer, logician, and engineer who made important and influential discoveries in many branches of mathematics. He is the one who figured out the Konigsberg theory. 

How to figure out if a network is traversable 

Networks are only traversable if the nodes are all even. 

If a network has two odd nodes it will still be traversable but it has to start at an odd node and finish at an odd node as well.  

If a network has more than two odd nodes it will not be transferable. 

Below are examples of traversable and non-traversable networks 

To figure out if a node is odd or even all you have to do is count the number of lines going into a certain node. 

For example; node A has 2 lines going into it. 2 is an even number so this node is even. Node B has 3 lines going into it and 3 is an odd number so this is an odd node. 

Before reading this did you ever hear about Leonhard Euler?