Can I Get There from Here? For this program, you will write a C++ Program to represent a travel network. This travel network will use an array of linked lists as its primary storage structure. This type of storage structure is typically called an adjacency list. Please note: this write-up was originally taken from a non-C++ assignment. Any reference to non-C++ items were not properly translated into C++. Such items should use their C++ counterparts. Assume you have a small airline that flies planes between a small number of airports. Each airport will be given a number. If a plane flies from airport X to airport Y, the network will have an edge from X to Y. Below are a number of drawings that could represent this idea. The airports are represented by the circled numbers, the edges are represented by the arrows. Consider the first drawing. It has 6 airports. It has a plane that flies from airport 1 to airport 2. Three planes fly from airport 2, one to airport 3, one to airport 4 and one to airport 5. No planes leave from airport 3 or from airport 5 (yes, it would be stupid to strand planes at those airports, but ignore that fact for now). Planes fly from airport 4 to airports 5 and 6. Finally, planes fly from airport 6 to airport 3. In an adjacency list, each location/airport needs a list of those locations/airports that one can get to in one move/flight. In this program, we need a list for each airport. If the travel network has N airports, the array will have N linked lists, one for each airport. If airport X has planes flying to 3 different airports, the linked list for airport X would have 3 nodes. Consider the following image showing a travel network and an adjacency list: There are 5 airports, so we have an array of 5 linked lists. Since Airport 3 can fly planes to two Airports, namely Airport 1 and Airport 4, the linked list for Airport 3 has two nodes: one node containing the value 1; another node containing the value 4. Program Input and Commands The input for the operations will come from standard input and from files. The input will initially come from standard input. If the user specified the f command, your program will then read input from a file. See the description below for more details. The commands are to follow the descriptions given below. Note: that the form could be any integer number and it will NOT be enclosed in angle brackets. is just a notation to specify and integer value. The integer value is to be input on the same line as the command character. If the first character on the line is not one of the following characters, print an error message and ignore the rest of the information on that line. - quit the program immediately. ? - display a list of the commands the user can enter for the program. # - ignore this line of input. Treat the line of input as a comment t - display a message stating whether a person can travel from airport to airport in one or more flights. - remove all values from the traffic network and resize the array to contain the number of airports as indicated by the given integer value. The value of the integer must be greater than zero. The airports will be numbered from 1 to the given integer value. Be sure to deallocate all unused memory as part of this command. i - insert the edge to indicate a plane flies from airport to airport . d - delete the edge that indicates a plane flying from airport to airport . l - list all the items contained in the travel network. First display all of the airports (if any) that can be reached from the airport #1 in one flight (that have an edge in the network), followed by all the airports (if any) that can be reached from airport #2 in one flight, etc. f - open the file indicated by the (assume it is in the current directory) and read commands from this file. When the end of the file is reached, continue reading commands from previous input source. This must be handled using recursion. Beware of a possible case of an infinite recursive loop, the f command is may not call a file that is currently in use. Initially your program should have the array to hold 10 airports (numbered 1 to 10). If a command specifies an airport outside of the current valid range, print an error message and ignore the command. The code given in proj6Base.cpp should provide the basics on reading input. You will need to do some cutting and pasting of code to read in input for all commands. The input is properly read in for the t and f commands. It is assumed that you can determine the code for the rest of the commands by looking at the code those these two commands. Travel Algorithm and the Airport Object To determine if a person can travel from airport X to airport Y in one or more flights, a recursive depthfirst-search algorithm must be used. For this algorithm to work, we will need to be able to mark each airport as visited. Setting up an Airport class is required. This object will contain all of the data that one airport knows (the head of the linked list for the airports adjacency list and the object will also contain a Boolean value to determine if an airport has been visited or not) and the methods to use that data. The travel network MUST be a dynamic array of these Airport objects. The adjacency list will also need a Node class/object to store the linked list information. The pseudo code for this algorithm is as shown below. Note it is valid to ask, can I to go from airport X to airport X in one or more flights. It really asks, If I leave airport X, can I return to it? This algorithm is recursive and you MUST use this recursive algorithm in your program. void depthFirstSearchHelper (int x, int y) { mark all airports as unvisited; if ( dfs (x, y) = = TRUE) print (You can get from airport + x + to airport + y + in one or more flights); else print (You can NOT get from airport + x + to airport + y + in one or more flights); } boolean dfs (int a, int b) { for (each airport c that can be reached from a in one flight) { if (c = = b) return TRUE; if ( airport c is unvisited ) { mark airport c as visited; if ( dfs (c, b) = = TRUE ) return TRUE; } } return FALSE; } The FILE Command: f The f command may seem difficult to implement at first, but it has a creative solution that you are to use. The code in the file Proj6Base.cpp is intended to give you an idea on how this solution is to be implemented. First note that main( ), is extremely short. It just creates an instance of the TravelNetwork class and calls the processCommandLoop( ) method with an value of FILE* that reads from standard input. The method processCommandLoop( ) reads from the input source specified by the parameter and determines the which command is being invoked. When the f command is invoked, it is to open the file specified by the command, create a new instance of FILE* that reads from this file. Then make a recursive call to processCommandLoop( ) with this new instance of the FILE* so the next line of input comes from the specified file instead of where the previous command came from. When the end of a file is reached, the program is to revert back to the previous input source that contained the f command. This previous input source could be standard input or a file. By making these calls recursively, reverting back to the previous input source is a complete no-brainer. However, this can cause an infinite loop if you try to access a file that your program is already reading from. Consider this scenario. Assume the user enters a command from standard input to start reading from file A. However; file A tells you to read from file B, file B tells you to read from file C, and file C tells you to read from file A. Since you always start reading from the top of the file, when file C eventually tells the program to read from file A, the program will reprocess the command to read from file B, which will reprocess the command to read from file C, which will reprocess the command to read from file A, which will reprocess the command to read from file B, which will reprocess the command to read from file C, which will reprocess the command to read from file A, which will reprocess In order to stop this, you are required to maintain a linked list of file names. Before the f command attempts to create a new instance of FILE* that read from file X, the f command is to check if the linked list of file names already contains the name of X. If the name X already exists in the linked list, the f command will NOT create a new instance of FILE* and it will NOT make the recursive call to processCommandLoop( ). If the name X does not exist in the linked list, the f command will add the name X to the linked list before making the recursive call to processCommandLoop( ) and it must remove the name X from the linked list after the call to processCommandLoop( ) returns. You are responsible to write the code for this linked list yourself. Note that this will most likely be a linked list of Strings, while each airports adjacency list will most likely be a linked list of integers. Classes You Must Write First you are to write a class called Airport. This class is to contain everything that is known about a specific Airport. This MUST include the airports adjacency list and the visited status for the Depth First Search. Next you are to write a list class. You are encouraged to name the class MyList as the name List is already used in the C++ Standard Template Libraries. Please note that your list class will need another class for the nodes in the list. Thus you must write a class called MyNode also. For your list class, in addition to the normal insertValue( ) and deleteValue( ) operations, you may want to write operations such as getNumberOfCurrentsValues( ) and getNthValue( ). The TravelNetwork class has been started for you. This class must contain the array of Airports and the linked list of filenames for the in-use files needed for the f command. All data members (or instance variables) must be made private. Failure to do this will result is a severe reductions of points for the project. You are not allowed to use any of the classes from the C++ Standard Template Libraries in this program. These classes include ArrayList, Vector, LinkedList, List, Set, Stack, HashMap, etc. If you need such a class, you are to write it yourself. These are sometimes called the C++ Standard Container Library. #include #include #include class TravelNetwork { private: // Create the Data Members for the Travel Network here public: // Use a constructor to initialize the Data Members for Travel Network TravelNetwork() { } // The main loop for reading in input void processCommandLoop (FILE* inFile) { char buffer[300]; char* input; input = fgets ( buffer, 300, inFile ); // get a line of input // loop until all lines are read from the input while (input != NULL) { // process each line of input using the strtok functions char* command; command = strtok (input , " \t"); printf ("*%s* ", command); if ( command == NULL ) printf ("Blank Line "); else if ( strcmp (command, "q") == 0) exit(1); else if ( strcmp (command, "?") == 0) showCommands(); else if ( strcmp (command, "t") == 0) doTravel(); else if ( strcmp (command, "r") == 0) doResize(); else if ( strcmp (command, "i") == 0) doInsert(); else if ( strcmp (command, "d") == 0) doDelete(); else if ( strcmp (command, "l") == 0) doList(); else if ( strcmp (command, "f") == 0) doFile(); else if ( strcmp (command, "#") == 0) ; else printf ("Command is not known: %s ", command); input = fgets ( buffer, 300, inFile ); // get the next line of input } } void showCommands() { printf ("The commands for this project are: "); printf (" q "); printf (" ? "); printf (" # "); printf (" t "); printf (" r "); printf (" i "); printf (" d "); printf (" l "); printf (" f "); } void doTravel() { int val1 = 0; int val2 = 0; // get an integer value from the input char* next = strtok (NULL, " \t"); if ( next == NULL ) { printf ("Integer value expected "); return; } val1 = atoi ( next ); if ( val1 == 0 && strcmp (next, "0") != 0) { printf ("Integer value expected "); return; } // get another integer value from the input next = strtok (NULL, " \t"); if ( next == NULL ) { printf ("Integer value expected "); return; } val2 = atoi ( next ); if ( val2 == 0 && strcmp (next, "0") != 0) { printf ("Integer value expected "); return; } printf ("Performing the Travel Command from %d to %d ", val1, val2); } void doResize() { int val1 = 0; printf ("Performing the Resize Command with %d ", val1 ); } void doInsert() { } void doDelete() { } void doList() { } void doFile() { // get a filename from the input char* fname = strtok (NULL, " \t"); if ( fname == NULL ) { printf ("Filename expected "); return; } printf ("Performing the File command with file: %s ", fname); // next steps: (if any step fails: print an error message and return ) // 1. verify the file name is not currently in use // 2. open the file using fopen creating a new instance of FILE* // 3. recursively call processCommandLoop() with this new instance of FILE* as the parameter // 4. close the file when processCommandLoop() returns } }; int main (int argc, char** argv) { // set up the variable inFile to read from standard input FILE* inFile = stdin; // set up the data needed for the airport adjcency list TravelNetwork airportData; // call the method that reads and parses the input airportData.processCommandLoop (inFile); printf ("Goodbye "); return 1; }