CS 1410 Introduction to Computer Science ­ CS2 Assignment #1 solution




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Problem description
Assume that you are working for Google and you want to write a program to analyze the
trends of users’ queries, e.g. what are the most frequent search terms. This program accepts
input as a text file named input.txt containing search terms, each term is on a single line. Its
output is a text file named output.txt which lists all distinct terms in the input file with their
corresponding frequencies sorted decreasingly. Each term and its frequency are written on
one line. To make the processing more efficient, in the input and output files, a search term is
encoded as an unique, integral ID rather than its character sequence.
0 3
2 2
1 1
3 1
Since Google receives billions of queries each day, your program should run as fast and use
as little memory as possible. In this assignment, your program is expected to be able to
process the provided input file with a million (1,000,000) lines and ten thousand (10,000)
distinct search terms within 10 minutes.
The following solution is potentially able to achieve that requirement. First, you will store all
the distinct search terms and their frequencies in an array sorted by those terms. When you
read a search term from the input file, you will use the binary search algorithm to look for that
term in that array. If you find the term, just increase its frequency. If it is not there, you will
insert it into the array at its proper location to keep the array sorted. After reading the input
file, you sort the array, in descending order, by frequency and write its elements to the output
Programming tasks
Now, design and implement the aforementioned ideas with the following instructions.
Task 1 (10 points). Declare a class TermTable to store all distinct search terms and their
frequencies in two arrays of 10,000 elements: one for the terms (i.e., term array) and one for
their corresponding frequencies (i.e., frequency array). This class also has a field (e.g., a data
member) to store the current number of terms stored in those arrays. The default constructor
assigns 0 to that field and to all elements of the two arrays.
Task 2 (10 points). Implement a “binarySearch” method in class TermTable. This method
uses the binary search algorithm to look for a search term in the term array.
Task 3 (10 points). Implement an “insert” method in class TermTable to insert a new term to
its two arrays (suggest to change it to the following: its term array and insert its count (e.g., 1)
to the corresponding frequency array). In other words, this method increases the current
number of terms, assigns the given term to the corresponding location in the term array,
assigns 1 to the corresponding location in the frequency array, and shifts the elements after
the inserted locations to their proper locations (e.g., the next locations) to keep all terms
Task 4 (10 points). Implement a “sort” method in class TermTable to sort the term and
frequency arrays descendingly by the frequencies.
Task 5 (10 points). Implement the main function to read all terms in the input file, process
them (i.e. search each term in the TermTable, update its frequency if found or insert it if not
found), and write the distinct terms and their frequencies sorted in the descending order to the
To read and write files, you could use the following code snippets:
Reading file:
ifstream fin(“input.txt”);
while (fin >> term) {
// do something with term here
Writing file:
ofstream fout(“output.txt”);
// to write a value x to fout, e.g. you could use fout << x;
You should submit your solution on Canvas as a cpp file named as
Firstname_Lastname_HW1.cpp. For example, if your name is Adam Smith, the submitted file
will be Adam_Smith_HW1.cpp