Programming Assignment 5 - Undo-Redo

See the assignment turn-in page (last modified on 11 September 2001) for instructions on turning in your assignment.

1. node name - create a node with the label name. Should print an error message if a node with the label name already exists in the graph. The new node does not have an edge to any other node in the graph.

2. edge name₁ name₂ - create an edge between the node with label name₁ and the node with label name₂; name₁ need not be different than name₂. If an edge already exists between name₁ and name₂, do nothing; if name₁ or name₂ don't exist, print an informative error message.

3. print - print the nodes and edges in the current graph, with the following format:
   name name₁, name₂, . . .

   where name is a node's label and name_i is the label of a node to which name has an edge. The information on each node should appear on one line; every node should have its information printed. The list of connected nodes should appear in alphabetical order from left to right, and the nodes should be printed in alphabetical order.

4. undo - Undo the effects of the most recent effective node or edge command; print an error message if there is no effective command to undo. The most recent effective command undone becomes an inactive command.

5. redo - Redo the most recent inactive command (which can only be a node or edge command); print an error message if there's no inactive command to redo. The most recent inactive command redone becomes an effective command.

Command input comes from standard-in; command output (if any) goes to standard-out; error output goes to standard-error. Each command fits on one line of input and each line of input contains at most one command.

Each node or edge command entered from the command-line deletes all inactive commands.

A name is any maximal sequence of non-space characters. Case is not significant in node labels; however node labels should be output with exactly the same case is they were input in a node command. For example, the label ALPHA is the same as the label alpha; however, if the label Alpha was input, then the label Alpha must be output. "Alphabetic order" should be extended to include the whole ASCII collating sequence.