helloformula for finding no of trees in a network graph??

Dear student,

A network is a collection of points, called vertices, and a collection of lines, called arcs, connecting these points. A network is traversable if you can trace each arc exactly once by beginning at some point and not lifting your pencil from the paper. The problem of crossing each bridge exactly once reduces to one of traversing the network representing these bridges.

Euler made the remarkable discovery that whether a network is traversable depends on the number of odd vertices. In the Königsberg network, there are an odd number of arcs at point A, so A is called an odd vertex. If the number of arcs meeting at a point is even, the point is called an even vertex. Euler found that the only traversable networks are those that have either no odd vertices or exactly two odd vertices. Since the Königsberg network has four odd vertices, it is not traversable. Therefore, it is not possible to take a walk over the bridges of Königsberg and cross each bridge only once.

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