adventofcode2024/day_02/src/main.rs

// https://adventofcode.com/2024/day/2
//
// run command: `cargo run ./input.txt`

use std::env;
use std::error::Error;
use std::fs::File;
use std::io::{BufReader, prelude::*};
use std::str::FromStr;

/// Parse a report into a Vec<T>
fn parse_report<T>(line: &str) -> Result<Vec<T>, <T as FromStr>::Err>
where
    T: FromStr,
{
    let parsed_line = line
        .split(char::is_whitespace)
        .map(|v| v.parse())
        .collect::<Result<Vec<T>, _>>()?;
    Ok(parsed_line)
}

#[derive(Eq, PartialEq)]
enum LevelTransitionState {
    Asc,
    Desc,
    Bad,
    Dampened,
}

fn compare_levels(curr_level: i64, next_level: i64) -> LevelTransitionState {
    let level_diff = next_level - curr_level;

    // If the diff is 0 or greater than 3, return bad stat
    if level_diff == 0 || level_diff.abs() > 3 {
        return LevelTransitionState::Bad;
    }
    // If great than zero they are ascending
    if level_diff > 0 {
        return LevelTransitionState::Asc;
    }
    //Else we're descending
    return LevelTransitionState::Desc;
}

fn is_report_safe(report: Vec<i64>) -> bool {
    // Turn the report into a bunch of states for each adjacent pair in the report
    let report: Vec<LevelTransitionState> = report
        .windows(2)
        .map(|l| compare_levels(l[0], l[1]))
        .collect();

    // Setup the loop by checking the first start as a special case
    let mut prev_state = &report[0];
    if prev_state == &LevelTransitionState::Bad {
        return false;
    }

    // Check each state
    for level_state in report[1..].iter() {
        // If bad, then it's just bad
        if level_state == &LevelTransitionState::Bad {
            return false;
        }

        // If the states aren't the same as the prev, it must
        // have changed direction
        if level_state != prev_state {
            return false;
        }

        // Setup for next iteration
        prev_state = level_state;
    }
    return true;
}

// let mut modified_report: Vec<Option<i64>> = vec![None];
// let mut tmp_report: Vec<Option<i64>> = report.iter().map(|v| Some(*v)).collect();
// modified_report.append(&mut tmp_report);
// modified_report.push(None);
// dbg!(modified_report);

// let states = Vec::new();
// for window in modified_report.windows(3) {
//     let window_tuple = (window[0], window[1], window[2]);
//     let state = match window_tuple {
//         (None, Some(curr), Some(next)) => {
//             let diff = curr
//         },
//         (Some(prev), Some(curr), Some(next)) => (),
//         (Some(prev), Some(curr), None) => (),
//         _ => panic!("This should never happen!"),
//     }
//     states.push(state);
// }

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_file = File::open(input_file_string)?;
    let input_reader = BufReader::new(input_file);

    let mut accumulator = 0;
    for line in input_reader.lines() {
        let line = line?;
        let parsed_report: Vec<i64> = parse_report(&line)?;
        if is_report_safe(parsed_report) {
            accumulator += 1;
        }
    }

    println!("Number of SAFE reports: {}", accumulator);

    Ok(())
}