3. When is a graph a tree? Write a program in C++ that will read from a file specified on the command line and determine from the graph's adjacency matrix whether or not it is a tree. Example: ./a.out graph.txt Output: The graph is a tree! Contents of graph.txt will be something like this: 5 0 1 0 0 0 1 0 1 1 1 0 1 0 0 0 0 1 0 0 0 0 1 0 0 0