3. When is a graph a tree? Write a program 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 01000 1 0 1 1 1 01000 01000 01000 To be graded, your program must be in your pgm and named precisely as 3.cpp