CS 3 lab – ZOMBIE-POCALYPSE
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CS 3 lab – ZOMBIE-POCALYPSE
1 Introduction
In this assignment you will use a computer program to help investigate the
pressing question: How long might I survive once the zombie-pocalypse starts?
This program will require you to utilize the following knowledge and skills:
for and while loops
conditionals
variables
input and output
basic arrays
simple algorithms
2 The Problem In a population of N people of which k are initially zombies, how many nights are required before the entire population (all N people) become zombies if the following conditions hold: Zombies only come out at night Being bitten by a zombie turns a human into a zombie Each zombie randomly chooses one person (zombie or human) from the population per night and bites them. (A zombie may bite another zombie but this has no effect, other than wasting that zombie’s bite for that night). On any given night, a zombie (being dumb) may even choose to bite itself which has no effect. A human who is bitten during a particular night and thus becomes a zombie should not bite anyone on that same night. They must wait until the next night to start biting people.Manipulate C-string variables (variables of type char*)
3 Setting up the Solution
While we can attempt to solve this problem analytically, let us instead use the
computer to "simulate" the problem to find the answer. Suppose we have an
array, pop, of length N that stores bool's representing the population, where the
i-th entry represents person i from the population. pop[i] will equal true if that
person IS a zombie and false, otherwise. The first k entries in the array will be
zombies while the remaining N-k will be human. For each zombie we can
randomly choose someone to bite (who may or may not already be a zombie),
changing them to a zombie if they were human. This would represent one night.
We could repeat this process on a second night, third night, fourth night, and so
on, counting the number of nights it takes until the entire population is a
zombie.
By using the computers random number generator we can simulate zombie bites
and count how many nights it takes until the population is all zombies. However,
the answer we obtain would be largely influenced by the random number
generation, since the numbers we generate will determine if a zombie bites a
human or another zombie (and thus another human is safe). We can easily see
that if the zombies get "lucky" (from the zombie's perspective), it may take a
small number of nights to bite all remaining humans while an "unlucky"
sequence of random values may mean a large number of nights before the
population is all zombies, since they end up biting each other more often. To
account for this issue, we will use the law of large numbers to perform not just 1
simulation of the zombi-pocalypse, but MANY (say, M). We can then use the
average number of nights taken for each of the M simulations of the zombie-
pocalypse to arrive at our answer. In addition, it may be interesting to find the
range of answers over the M simulations, meaning what was the smallest
(minimum) number of nights any zombie-pocalypse simulation required and
what was the largest (maximum) number of nights any zombie-pocalypse
simulation required. You should track these values as you perform the
simulations and output them with the average.
To control the repeatability of our random simulations we will allow a seed value
to be provided by the user. This seed value will be supplied to the random
number generator so that execution of the program multiple times using the
same seed will result in the same sequence of random numbers (and thus same
answer).
4 Input/Output
Based on the description above your program should take in the following input
values (in the order shown) from the user. The inputs may be typed on one line
and separated by whitespace.
N, the total population
k, the number of initial zombies (Exit the program if the user enters k > N)
M, the number of simulations of the zombie-pocalypse to run and
average the results
s, the seed for the random number generator
Your output should be the average, maximum and minimum number of nights
until the entire population is a zombie. It should be formatted as:
Average Nights: avg-nights
Max Nights: max-nights
Min Nights: min-nights
Here are three sample runs of the program: the emphasized text is the part that
the user typed in and the $ is the command-line prompt.
$ ./zombies
Enter the following: N k M seed
20 2 10000 137957
Average Nights: 7.
Max Nights: 16
Min Nights: 4
$ ./zombies
Enter the following: N k M seed
100 5 10000 137957
Average Nights: 10.
Max Nights: 19
Min Nights: 7
$ ./zombies
Enter the following: N k M seed
100 10 10000 371
Average Nights: 8.
Max Nights: 18
Min Nights: 6
5 Skeleton: We have provided a skeleton (starter code) in Vocareum.
You'll notice we declare an array pop to represent the population. In a normal
program, the size of this array would match the population size entered by the
user. However, since statically declared arrays must be of a constant size (known
at compile time), we allocate a LARGE array that will be big enough to handle the
large population we will test your code with. In your program you should only
use the first N locations in that array.
6 Readme: Answer the experimental questions that are listed in the readme file. Open readme.txt in Vocareum to read the questions and answer them. Please write your answers in the same file readme.txt
7 Style: You must follow all of the code style guidelines posted here. http://bytes.usc.edu/cs103/coursework/style/
8 Submit: Use Vocareum to submit your code and readme file. It will run some basic tests to check your formatting. To check it more exhaustively, it would be a good idea for you to try running it on additional test cases.
9 Q&A:
Q: Which k people should start as zombies?
A: Your code should work in a way where it does not matter. However, it is
likely easiest to let the first k entries in the people array be the zombies.
Q: Can we use functions for this assignment?
A: You can if you like, but they are not required, and don't help in any
serious way.
Q: What if the user enters 0, a negative number, a decimal, or text for N, k,
M, or seed?
A: For this assignment, assume the user only enters positive integers.
Q: How do you compute minimums and maximums?
A: Section 4.7.4 has a closely related example. Store some memory, and
every time you see a new value, compare it to see if it's a record, and if so,
remember it. Instead of initializing to the first entry like the examples, it may
be convenient to initialize the max/min to placeholder values like -1 and
INT_MAX (from <climits>).
Q: Can we use additional arrays for this assignment?
A: You can correctly solve this problem with only the array that is already
declared in the skeleton file. However, if you want to create one more array
(for a total of 2) you are welcome to do so. You should not need more than
2.
Q: Do we have to match the formatting and text exactly?
A: Generally yes. Your output must include a line containing only Nights:
your-answer. The automatic grader will ignore other text. However, it is
good habit to remove any debug or extra cout statements you might have
added along the way before submitting your code.
Credit to David Kempe for posing a version of this problem. Assignment created by Mark Redekopp.