An Euler tour of a connected, directed graph G = (V, E) is a cycle that traverses each edge of G exactly once, although it may visit a vertex more than once.
a. Show that G has an Euler tour if and only if in-degree (v) = out-degree (v) for each vertex v ¬ V.
b. Describe an O (E)-time algorithm to find an Euler tour of G if one exists.