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# Lab Assignment 07

 Topic: Phone List Source Code: phone.cpp In-Class Day: Thursday, 22 March 2012, 10:00am Submission Deadline: Friday, 23 March 2012, 11:59pm Techniques: Use of strings and system sort.

### Collaboration Policy

The pre-lab requirement must be completed and submitted individually.

The remainder of the lab activity should be completed working in pairs. One person should submit the result, making sure that both partners' names are clearly identified in that submission.

## Pre-Lab Requirement

Read the complete problem description and then determine what the expected output should be if given the following input:

 Prelab input: Prelab output: 3 3 9777039 9772444 3149777039 3 012 12 210 4 3 4 1234 4321

# Phone List

Given a list of phone numbers, determine if it is consistent in the sense that no number is the prefix of another. Let's say the phone catalogue listed these numbers:

• Emergency 911
• Alice 97 625 999
• Bob 91 12 54 26
In this case, it's not possible to call Bob, because the central would direct your call to the emergency line as soon as you had dialled the first three digits of Bob's phone number. So this list would not be consistent.

Input: The first line of input gives a single integer, 1≤t<40, the number of test cases. Each test case starts with n, the number of phone numbers, on a separate line, 1<n<10000. Then follows n lines with one unique phone number on each line. A phone number is a sequence of at most ten digits.

Output: For each test case, output "YES" if hte list is consistent, or "NO" otherwise.

 Example input: Example output: 2 3 911 97625999 91125426 5 113 12340 123440 12345 98346 NOYES

# Hints

Although this problem is about "numbers", you should store all of these as strings.

Then, the key to efficiency for this problem is to first sort the list of strings, and then you can determine consistency by checking whether any entry is a prefix of the one immediately following it.

Useful documentation:

• Sorting can be done with sort function from the <algorithm> library, for arrays and vectors, or the sort method of the list class.

Syntax for sorting array A of length n is: sort(A, A+n).

Syntax for sorting vector V: sort(V.begin(), V.end()).

Syntax for sorting list L: L.sort().

Michael Goldwasser
CSCI 180, Spring 2012