adventofcode2024/day_03/src/main.rs

//https://adventofcode.com/2024/day/3
//
// Run command: cargo run ./input.txt

use core::ops::Mul;
use core::panic;
use std::env;
use std::error::Error;
use std::fs::File;
use std::io::{BufReader, prelude::*};
use std::str::FromStr;
#[derive(Eq, PartialEq, Clone, Debug)]
enum Token {
    Text(String),
    Number(String),
    Comma,
    OpenParenthesis,
    CloseParenthesis,
    SpecialChar(char),
    Whitespace,
    NewLine,
}

fn is_mul_text_token(text_token: &str) -> bool {
    if text_token.ends_with("mul") {
        true
    } else {
        false
    }
}

fn tokenize(input_str: String) -> Vec<Token> {
    let mut tokens: Vec<Token> = Vec::new();
    let mut chars = input_str.chars().peekable();
    while let Some(c) = chars.next() {
        let token = match c {
            // Text Numeric
            _ if char::is_alphabetic(c) => {
                let mut text = c.to_string();
                while let Some(alphabetic_char) = chars.next_if(|p| p.is_alphabetic()) {
                    text.push(alphabetic_char)
                }
                Token::Text(text)
            }
            // Numbers
            _ if char::is_numeric(c) => {
                let mut number = c.to_string();
                while let Some(numeric_char) = chars.next_if(|p| p.is_numeric()) {
                    number.push(numeric_char)
                }
                Token::Number(number)
            }
            // whitespace
            _ if char::is_whitespace(c) => {
                while chars.next_if(|p| p.is_whitespace()).is_some() {}
                Token::Whitespace
            }
            _ if c == ',' => Token::Comma,
            _ if c == '(' => Token::OpenParenthesis,
            _ if c == ')' => Token::CloseParenthesis,
            _ if c == '\n' => Token::NewLine,
            _ => Token::SpecialChar(c),
        };
        tokens.push(token);
    }
    tokens
}

#[derive(Debug)]
struct MulOp {
    lhs: String,
    rhs: String,
}

impl MulOp {
    pub fn multiple<T>(&self) -> Result<<T as Mul>::Output, <T as FromStr>::Err>
    where
        T: FromStr + Mul,
    {
        let lhs: T = self.lhs.parse()?;
        let rhs: T = self.rhs.parse()?;
        Ok(lhs * rhs)
    }
}

fn parse_tokens(tokens: &Vec<Token>) -> Vec<MulOp> {
    let mut tokens = tokens.iter().peekable();
    let mut muls: Vec<MulOp> = Vec::new();
    while let Some(token) = tokens.next() {
        match token {
            Token::Text(t) => {
                if is_mul_text_token(t) {
                    // Take OpenParenthesis or continue
                    if !tokens.next_if_eq(&&Token::OpenParenthesis).is_some() {
                        continue;
                    }
                    // Take Number or continue
                    let lhs = if let Some(Token::Number(lhs)) =
                        tokens.next_if(|v| matches!(v, Token::Number(_)))
                    {
                        lhs.to_owned()
                    } else {
                        continue;
                    };
                    // Take Comma or continue
                    if !tokens.next_if_eq(&&Token::Comma).is_some() {
                        continue;
                    }
                    // Take Number or continue
                    let rhs = if let Some(Token::Number(rhs)) =
                        tokens.next_if(|v: &&Token| matches!(v, Token::Number(_)))
                    {
                        rhs.to_owned()
                    } else {
                        continue;
                    };
                    // Take CloseParenthesis or continue
                    if !tokens.next_if_eq(&&Token::CloseParenthesis).is_some() {
                        continue;
                    }
                    muls.push(MulOp { lhs, rhs });
                }
            }
            _ => (),
        }
    }
    muls
}

fn main() -> Result<(), Box<dyn Error>> {
    // Handle command input
    let args: Vec<String> = env::args().collect();
    if args.len() != 2 {
        panic!(
            "{} must be run with a single argument of files name!",
            &args[0]
        )
    }
    let input_file_string = &args[1];

    let input_buffer = BufReader::new(File::open(input_file_string)?);

    let mut tokens: Vec<Token> = Vec::new();
    for line in input_buffer.lines() {
        tokens.append(&mut tokenize(line? + "\n"));
    }
    //println!("{:?}", tokens);

    let muls = parse_tokens(&tokens);
    //println!("{:?}", muls);

    let mut accumulator: i64 = 0;
    for mul in muls {
        accumulator += mul.multiple::<i64>()?;
    }

    println!("Answer: {}", accumulator);

    Ok(())
}