# Lab Assignment 5

 Topic: Symmetric Order (again) Source Code: order.cpp Live Archive Ref#: 3055 In-Class Day: Thursday, Oct. 27, 2011 Submission Deadline: Sunday, Oct. 30, 2011 Techniques: Use of a vector.

# Symmetric Order (again)

In your job at Albatross Circus Management (yes, it's run by a bunch of clowns), you have just finished writing a program whose output is a list of names in nondescending order by length (so that each name is at least as long as the one preceding it). However, your boss does not like the way the output looks, and instead wants the output to appear more symmetric, with the shorter strings at the top and bottom and the longer strings in the middle. His rule is that each pair of names belongs on opposite ends of the list, and the first name in the pair is always in the top part of the list. In the first example set below, Bo and Pat are the first pair, Jean and Kevin the second pair, etc.

Input: The input consists of one or more sets of strings, followed by a final line containing only the value 0. Each set starts with a line containing an integer, n, which is the number of strings in the set, followed by n strings, one per line, sorted in nondescending order by length. None of the strings contain spaces. There is at least one and no more than 15 strings per set.  Each string is at most 25 characters long.

Output: For each input set print "SET n" on a line, where n starts at 1, followed by the output set as shown in the sample output.

 Example input: Example output: 7 Bo Pat Jean Kevin Claude William Marybeth 6 Jim Ben Zoe Joey Frederick Annabelle 5 John Bill Fran Stan Cece 0 SET 1 Bo Jean Claude Marybeth William Kevin Pat SET 2 Jim Zoe Frederick Annabelle Joey Ben SET 3 John Fran Cece Stan Bill

# Hints

Look familiar? Yes, we already solved this problem two weeks ago when using stacks. At that time, I described a bizarre way that worked by printing one, pushing the next to a stack, printing the third, pushing the fourth and so on. Although that approach worked, I can all but guarantee that not a single team would have bothered to solve it that way.

This problem can be solved quite easily with a vector. Start by reading all the strings into a vector, using the given order. Then, to get the output in the desired order, write one loop to print out all elements of the vector that have even index (i.e., v[0], v[2], v[4], ...). Then write a second loop that starts at the end moving backward while printing all items that have an odd index (i.e., v[5], v[3], v[1]). The only care needed is to ensure that your loops execute the correct number of iterations.

So for today's lab, please redo this problem, this time using the std::vector class of the <vector> library. If you need a reminder, you can find online documentation regarding its usage. But its essentially an array that resizes as you push things to the back. Note, however, that the STL does use iterators with vectors, where our Vector.h class simply used integer indices, so you will need to be careful with a few of the differences.

### Pre-lab

No pre-lab this week, since it's the same as a previous lab.