4. (a) A company wishes to lay video cables to a number of locations
       such that a minimum amount of cable is used (consequently
       less cost in laying the cable, and in the cable itself).
       There are n locations and you are given the distances between pairs
       of locations. Describe an algorithm that will deliver a design 
       that uses a minimum amount of video cable. Note that your description
       of the algorithm can be in "structured English" or in Scheme.

                                                                12 Marks

   (b) The table below shows the distance between locations, and this is
       shown graphically in the accompanying diagram. It is assumed that there
       is no distance from a location to itself, and that if two locations
       are not adjacent then the corresponding table entry will be a dash 
       (and this can be considered as an infinite value). Show your solution 
       to this problem, and show how the design is constructed step by step
       by your algorithm.

                                                                8 Marks

                  1     2     3     4     5     6
               _____________________________________
               |     |     |     |     |     |     |
             1 |     |  6  |  1  |  5  |  -  |  -  |
               |     |     |     |     |     |     |
               -------------------------------------
               |     |     |     |     |     |     |
             2 |  6  |     |  5  |  -  |  3  |  -  |
               |     |     |     |     |     |     |
               -------------------------------------
               |     |     |     |     |     |     |
             3 |  1  |  5  |     |  5  |  6  |  4  |
               |     |     |     |     |     |     |
               -------------------------------------
               |     |     |     |     |     |     |
             4 |  5  |  -  |  5  |     |  -  |  2  |
               |     |     |     |     |     |     |
               -------------------------------------
               |     |     |     |     |     |     |
             5 |  -  |  3  |  6  |  -  |     |  6  |
               |     |     |     |     |     |     |
               -------------------------------------
               |     |     |     |     |     |     |
             6 |  -  |  -  |  4  |  2  |  6  |     |
               |     |     |     |     |     |     |
               -------------------------------------