Puzzle Part One:

Space on the sleigh is limited this year, and so Santa will be bringing his list as a digital copy. He needs to know how much space it will take up when stored.

It is common in many programming languages to provide a way to escapespecial characters in strings. For example, C, JavaScript, Perl, Python, and even PHP handle special characters in very similar ways.

However, it is important to realize the difference between the number of characters in the code representation of the string literal and the number of characters in the in-memory string itself.

For example:

• "" is 2 characters of code (the two double quotes), but the string contains zero characters.

• "abc" is 5 characters of code, but 3 characters in the string data.

• "aaa\"aaa" is 10 characters of code, but the string itself contains six "a" characters and a single, escaped quote character, for a total of 7 characters in the string data.

• "\x27" is 6 characters of code, but the string itself contains just one - an apostrophe ('), escaped using hexadecimal notation.

Santa's list is a file that contains many double-quoted string literals, one on each line. The only escape sequences used are \\ (which represents a single backslash), \" (which represents a lone double-quote character), and \x plus two hexadecimal characters (which represents a single character with that ASCII code).

Disregarding the whitespace in the file, what is the number of characters of code for string literals minus the number of characters in memory for the values of the strings in total for the entire file?

For example, given the four strings above, the total number of characters of string code (2 + 5 + 10 + 6 = 23) minus the total number of characters in memory for string values (0 + 3 + 7 + 1 = 11) is 23 - 11 = 12.

My Solution

• Include File Content: Reads the content of the "input.txt" file and stores it in the contents variable.

• Split Content into Lines: Divides the content into lines, creating a vector (Vec<&str>) named lines with each line as an element.

• Initialize Counters: Sets up two counters, literal_strings to count the length of literal strings, and memory_strings to count the length of memory strings.

• Create Regular Expression (Regex): Constructs a regular expression that searches for escape sequences like \x followed by two hexadecimal characters.

• Iterate Over Lines and Process Strings: Iterates through each line. literal_strings is increased by the length of the line without modifications. memory_strings is increased by the length of the line after applying certain transformations using the regular expression, then adjusted by subtracting 2.

• Print Results: Displays the total length of literal strings, the total length of memory strings, and the difference between them.

use regex::Regex;

fn main() {
    let contents = include_str!("../input.txt");
    let lines: Vec<&str> = contents.split_whitespace().collect();
    let mut literal_strings = 0;
    let mut memory_strings = 0;

    let regex = Regex::new(r"\\x[a-f0-9A-F]{2}").unwrap();

    for line in lines {
        literal_strings += line.len();

        memory_strings += regex
            .replace_all(line, "x")
            .replace("\\\\", "x")
            .replace("\\\"", "x")
            .len()
            - 2;
    }

    println!("{} literal_strings", literal_strings);
    println!("{} memory_strings", memory_strings);
    println!(
        "{} literal_strings - memory_strings",
        literal_strings - memory_strings
    );
}

input.txt (example):

""
"abc"
"aaa\"aaa"
"\x27"

Part Two:

Now, let's go the other way. In addition to finding the number of characters of code, you should now encode each code representation as a new string and find the number of characters of the new encoded representation, including the surrounding double quotes.

For example:

• "" encodes to "\"\"", an increase from 2 characters to 6.

• "abc" encodes to "\"abc\"", an increase from 5 characters to 9.

• "aaa\"aaa" encodes to "\"aaa\\\"aaa\"", an increase from 10 characters to 16.

• "\x27" encodes to "\"\\x27\"", an increase from 6 characters to 11.

Your task is to find the total number of characters to represent the newly encoded strings minus the number of characters of code in each original string literal. For example, for the strings above, the total encoded length (6 + 9 + 16 + 11 = 42) minus the characters in the original code representation (23, just like in the first part of this puzzle) is 42 - 23 = 19.

My Solution:

The second code snippet introduces a new counter called encoded_strings to keep track of the length of encoded strings. It includes additional processing steps for each line, replacing occurrences of "\" and """ with "xx". The results of the processing are then used to update the encoded_strings counter. Finally, the code prints the total length of literal strings, memory strings, the difference between them, the total length of encoded strings, and the difference between encoded and literal strings.

use regex::Regex;

fn main() {
    let contents = include_str!("../input.txt");
    let lines: Vec<&str> = contents.split_whitespace().collect();
    let mut literal_strings = 0;
    let mut memory_strings = 0;
    let mut encoded_strings = 0;

    let regex = Regex::new(r"\\x[a-f0-9A-F]{2}").unwrap();

    for line in lines {
        literal_strings += line.len();

        memory_strings += regex
            .replace_all(line, "x")
            .replace("\\\\", "x")
            .replace("\\\"", "x")
            .len()
            - 2;

        encoded_strings += &line.replace("\\", "xx").replace("\"", "xx").len() + 2;
    }

    println!("{} literal_strings", literal_strings);
    println!("{} memory_strings", memory_strings);
    println!(
        "{} literal_strings - memory_strings",
        literal_strings - memory_strings
    );
    println!("{} encoded_strings", encoded_strings);
    println!(
        "{} encoded_strings - literal_strings",
        encoded_strings - literal_strings
    );
}