The class WGraph has two constructors WGraph$()$ and WGraph$($String file$).$ The first one creates an empty graph and the second uses a file to initialize a graph. Graphs are encoded using the following format: the first line corresponds to two integers, separated by one space, that repre$-$ sent the $$source$"$ and the $$destination$"$ nodes.The second line of this file is a single integer n that indicates the number of nodes in the graph. Each vertex is labelled with a number in $[0,...,$ n $1],$ and each integer in $[0,...,$ n $1]$ represents one and only one vertex. The following lines respect the syntax $$n$1$ n$2$ w$,$ where n$1$ and n$2$ are integers representing the nodes connected by an edge, and w the weight of this edge.