Below is a partial $`$Graph$`$ class implementation. There is a method to add a vertex to the graph, $`$addVertex$`,$ but the code is missing functionality to add an edge or find a vertex. Modify the $`$Graph$`$ class to include methods to add an edge and find a vertex by its value. Specifically:

$`$addEdge$($key$1,$ key$2)`$

$*$ This method takes the key values of two vertices in the graph and adds an edge between them. If one or both of the vertices don$$t exist in the graph, the method should print a message, "One or more vertices not found." and do not add any edges.

$`$findVertex$($key$)`$

$*$ This method takes the key value of the vertex to search for, and if it$$s found in the graph, prints and returns the key values of its adjacent vertices.