关于后端:CSC-3002问题解答

CSC 3002 (Spring 2021) Assignment 1
Problem 1
Exercise 2.9:
The combinations function C(n, k) described in this chapter determines the number of ways
you can choose k values from a set of n elements, ignoring the order of the elements. If the order of
the value matters-so that, in the case of the coin example, choosing a quarter first and then a dime
is seen as distinct from choosing a dime and then a quarter-you need to use a different function,
which computes the number of permutations. This function is denoted as P(n, k), and has the
following mathematical formulation:
P(n, k) = n!
(n − k)!
Although this definition is mathematically correct, it is not well suited to implementation in practice
because the factorials involved can get much too large to store in an integer variable, even when the
answer is small. For example, if you tried to use this formula to calculate the number of ways to
select two cards from a standard 52 -card deck, you would end up trying to evaluate the following
fraction:
80, 658, 175, 170, 943, 878, 571, 660, 636, 856, 403, 766, 975, 289, 505, 440, 883, 277, 824, 000, 000, 000, 000
30, 414, 093, 201, 713, 378, 043, 612, 608, 166, 064, 768, 844, 377, 641, 568, 960, 512, 000, 000, 000, 000
even though the answer is the much more manageable 2652(52 × 51).
Write a function permutations (n, k) that computes the P(n, k) function without calling the
fact function. Part of your job in this problem is to figure out how to compute this value efficiently.
To do so, you will probably find it useful to play around with some relatively small values to get a
sense of how the factorials in the numerator and denominator of the formula behave.
Requirments & Hints:
Please fill in the TODO part of Permutations.cpp.
Problem 2
Exercise 3.20:
There is no gene for the human spirit. – Tagline for the 1997 film GATTACA
The genetic code for all living organisms is carried in its DNA-a molecule with the remarkable
capacity to replicate its own structure. The DNA molecule itself consists of a long strand of chemical
bases wound together with a similar strand in a double helix. DNA’s ability to replicate comes
from the fact that its four constituent bases-adenosine, cytosine, guanine, and thymine-combine
with each other only in the following ways:
• Cytosine on one strand links only with guanine on the other, and vice versa
• Adenosine links only with thymine, and vice versa.
Biologists abbreviate the names of the bases by writing only the initial letter: A, C, G, or T.
Inside the cell, a DNA strand acts as a template to which other DNA strands can attach
themselves. As an example, suppose that you have the following DNA strand, in which the position
of each base has been numbered as it would be in a C + + string:
Your mission in this exercise is to determine where a shorter DNA strand can attach itself to
the longer one. If, for example, you were trying to find a match for the strand
the rules for DNA dictate that this strand can bind to the longer one only at position 1:
By contrast, the strand
matches at either position 2 or position 7.
Write a function
int findDNAMatch (string s1, string s2, int start = 0) ;
that returns the first position at which the DNA strand s1 can attach to the strand s2. As in
the find method for the string class, the optional start parameter indicates the index position at
which the search should start. If there is no match, findDNAMatch should return -1.
Requirments & Hints:
Please fill in the TODO part of FindDNAMatch.cpp.
Problem 3
Exercise 4.8:
Even though comments are essential for human readers, the compiler simply ignores them. If
you are writing a compiler, you therefore need to be able to recognize and eliminate comments that
occur in a source file.
Write a function
void removeComments (istream & is, ostream & os)
that copies characters from the input stream is to the output stream os, except for characters
that appear inside C + + comments. Your implementation should recognize both comment
conventions:
• Any text beginning with /? and ending with ?/, possibly many lines later.
• Any text beginning with // and extending through the end of the line.
The real C + + compiler needs to check to make sure that these characters are not contained
inside quoted strings, but you should feel free to ignore that detail. The problem is tricky enough
as it stands.
Requirments & Hints:
Please fill in the TODO part of RemoveComments.cpp. You can prepare your test file under
the res folder in Stanford Library for testing. The generated results should print in the Stanford
console.
Problem 4
Exercise 4.9:
Books were bks and Robin Hood was Rbinhd. Little Goody Two Shoes lost her Os and so did
Goldilocks, and the former became a whisper, and the latter sounded like a key jiggled in a lck. It
was impossible to read”cockadoodledoo”aloud, and parents gave up reading to their children, and
some gave up reading altogether…. – James Thurber, The Wonderful O, 1957
In James Thurber’s children’s story The Wonderful O, the island of Ooroo is invaded by pirates
who set out to banish the letter O from the alphabet. Such censorship would be much easier with
modern technology. Write a program that asks the user for an input file, an output file, and a
string of letters to be eliminated. The program should then copy the input file to the output file,
deleting any of the letters that appear in the string of censored letters, no matter whether they
appear in uppercase or lowercase form.
As an example, suppose that you have a file containing the first few lines of Thurber’s novel, as
follows:
If you run your program with the input
it should write the following file:
If you try to get greedy and banish all the vowels by entering aeiou in response to the prompt,
the contents of the output file would be
Requirments & Hints:
Please fill in the TODO part of BanishLetters.cpp. The test file is named as TheWonderfulO.txt.
The prepared test file is provided under the res folder in Stanford Library for testing. The generated
new file will existed in the build content named as build-Assignment1-. . . .
Requirements for Assignment
I’ve provided a project named as Assignment1.pro. You should write TODO part in each cpp
file according to the problem requirements. The resources and test files are provided under res
folder such as P3RemoveComments.cpp and TheWonderfulO.txt. You can use them with relative
path directly after you compile the whole project. Finally, please pack your whole project files into
a single .zip file, name it using your student ID (e.g. if your student ID is 123456, hereby the file
should be named as 123456. zip ), and then submit the .zip file via BB system.
Please note that, the teaching assistant may ask you to explain the meaning of your program, to
ensure that the codes are indeed written by yourself. Please also note that we may check whether
your program is too similar to your fellow students’code using BB.
Please refer to the BB system for the assignment deadline. For each day of late submission, you
will obtain late penalty in the assignment marks. If you submit more than 3 days later than the
deadline, you will receive 0 in this assignment.
Marking scheme:
• 25% Marks will be given to students who have submitted the program on time.
• 25% Marks will be given to students who wrote the program that meet all the requirements
of the questions
• 25% Marks will be given to students who programs that can be compiled without errors.
• 25% Marks will be given to students whose programs produce the correct output if their
programs can be compiled.
Reminder: For windows users, please switch you input language to English before interacting
in Stanford console. Or, you will get no response.