CS 340 - Machine Problem 1

Find the Maze Path

Due: 11:59 pm on Thursday 9/14/2006 Monday 9/18/2006

For this assignment, you are to write a C++ program that will find a path in a given maze. The maze will consist of a 20x20 matrix. The path is to start at position 1,1 (upper left corner) of the maze and travel to some randomly determined ending position. The path can move to any open neighboring position in either a horizontal or vertical direction (but NOT diagonally).

The input for the maze will be given by a sequence of two integer values per line (separated by space characters). Each pair of values will be the coordinates of a position in the maze that is blocked (i.e. cannot be used in the path). The last pair of input values will be 1 1. Since the start position cannot be blocked (unless you want a very boring maze), it makes a good terminal value for the input. The input is to be read from standard input, so it can be entered at runtime or redirected from an input file. Before the input is read in, print a message such as Reading blocked maze positions, (end input with value "1 1").... If an input pair contains a value outside of the range of 1 to 20, print out an error message and ignore the input pair. After the input is finished being read in print out the maze in some readable form. Here is a sample data file. Note, there are three invalid position in the input.

The input may be give from standard input (in which you can use redirection to read from a file). The input can also be given via a command line argument. In this case, the user may list the names of one or more files after the name of the executable file. To read in the filenames from the command line, use the parameters to main typically named argc and argv. If more than one input file is given, you are to process all of the datafiles in the order they are given. If an input file is given via the command line, you are not to process input from standard input.

After the maze has been printed you are to find the path to five different ending positions. These ending positions must be randomly determined by your program (use the rand() function) and must not be blocked positions. Each path must be found twice, once using a stack (this will be a depth-first search) and once using a queue (this will be a breadth-first search). The path found by using a stack will (in most cases) be different than the path found by the queue. It is posible that that a path could not be found (i.e. part of the maze is completely blocked off from the start position). In this case print a message that no path could be found from the starting position to the ending position.

To use the stack, you would first push the start position onto the stack and then loop until either the stack becomes empty (no path to the end) or you encounter the end position. During each cycle of the loop, you find a single neighboring position to the position on the top of the stack that has not been visited. If such a position exists you push this neighboring position onto the stack. If such a position does not exist you pop the top position from the stack. Once the end position is found, the path from start to end are the positions currently on the stack.

To use the queue, you would first add the start position to the queue and then loop until either the queue becomes empty (no path to the end) or you encounter the end position. During each loop cycle, you are to remove the first position from the queue. Then add all neighboring positions that have not been visited to the queue. Once the end position has been found, the path from the start to the end is found by backtracking from the end position to the beginning position. To do this, at each visited position you must remember which position added it to the queue.

Once a position is pushed onto the stack or added to the queue, that position has been "visited. A visited position cannot get "unvisited while finding the current path.

Program Output Summary

  1. The initial message. Such as:
         Reading blocked maze positions, (end input with value "1 1")...

  2. Messages for any invalid input values.

  3. The maze showing the blocked positions

  4. For each of the 5 end positions,

    1. The end position
    2. The path found using the stack or message stating end position is not reachable.
    3. The path found using the queue or message stating end position is not reachable.

    The path can be shown by listing a sequence of positions in the maze (starting from position 1,1) or by showing the maze in a 20x20 grid which clearly showing the positions on the path and the blocked positions (a border around the maze is a good idea).

General Comments

The code for the queue and stack must be written by yourself and must use pointers. You will received zero points for this assignment if you use a library queue or stack (i.e. you don't write it yourself).

Your program must be written in good programming style. This includes (but is not limited to) meaningful identifier names, a file header at the beginning of each source code file, a function header at the beginning of the function, proper use of blank lines and indentation to aide in the reading of your code, explanatory "value-added" in-line comments, etc.

The work you turn in must be 100% done by yourself. You are not allowed to share code with any other persons (inside this class or not). You may discuss the project with other persons; however, you may not show any code you write to another person nor may you look at any other person's written code.

You are to submit this project using the CS Department's UNIX machine's turnin command. The project name for this assignment is mp1. Be sure to submit all source code and header files and makefile. Failure to turnin all required pieces will result in a lower grade for the assignment. The turnin command for this assignment is:

     turnin -c cs340 -p mp1 <file list>
where <file list> is the names of all files that you will submit for this program. You can use the turnin command multiple times; however, ever time you must submit all files needed for the program. To see which files you have submitted to turnin use the -v option with the turnin command as follows:
     turnin -c cs340 -p mp1 -v