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POTD30.1. Encrypted Messaging With Huffman Trees
Download and Extract
An initial setup of files is provided to you via a shell script: Download potd-q30
Using a terminal, extract the initial files by running the shell script you just downloaded (you
will need to navigate to the directory where you saved the file):
sh potd-q30.sh
Your files for this problem will be in the potd-q30 directory.
The Story
Thanks to your heroic adventures during your time so far in CS 225, the FBI and CIA have
requested your help. You are ready to accept their requests, Now, you must encrypt the
messages you send to them and decrypt all messages they have sent to you. With your
impressive understanding of trees from CS 225, you will utilize a trees provided to you by
these agencies to help you encrypt and decrupt messages. The type of tree they have
provided you is a huffman tree, which we will provide you with more information on below.
Your heroic efforts will also help you accept offers from Gooogle and Facebook who have
require you to send your replies to them using their own message encoding.
The Problem
You will utilize Huffman Encoding that is represented in a Huffman Tree in order to turn
strings into a secret binary encrypted message, and turn binary encrypted messages into
human readable strings. The Huffman Trees left paths represent a 0 in the binary message
and taking a right oath represents a 1. The exampe below can help clarify.
Complete the member function stringToBinary and binaryToString in the HuffmanUtils
file. More information is in the files
Example
In HuffmanUtils.cpp, a simple example of a huffman tree we can provide:
6
0 / \ 1
'E' 4
0 / \ 1
2 2
0 / \1 0/ \ 1
'S' 'R''C''T'
The numbers in each node represent character frequencies. The number on each edge
represent the direction taken on the tree. For instance to encode S, the value is 100.
NOTE: In the huffman tree, the FBI, CIA, Facebook, and Google have all decided based on
the functions you are writing to be optimal and not store the frequencies in each non-leaf
node since your code will not need to utilize the frequency values.
Some Tips About Strings
If you are not sure how to analyze each letter of a string in your code, here are a few ways
you can iterate over a string.
POTD 30
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string str = "cs225agent";
// Prints out every chracter in the string on a new line
for (const char& c : str) {
// NOTE: This method does not let you edit the inner elements in the string
std::cout << c << std::endl;
}
string str = "cs225agent";
// Print out every character in the string
for (char& c: str) {
std::cout << c << std::endl;
}
string str = "cs225agent";
// Another way to iteratore over characters in the string
for (size_t i = 0; i < str.length(); ++i) {
std::cout << str[i] << std::endl;
}
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