AoC Day 1 - Part 2

aoc-day-1-pt2.rs

use std::fs;
use std::io::{BufRead, BufReader};
use std::path::PathBuf;

const WORDS: [(&str, u32); 10] = [
    ("zero", 0),
    ("one", 1),
    ("two", 2),
    ("three", 3),
    ("four", 4),
    ("five", 5),
    ("six", 6),
    ("seven", 7),
    ("eight", 8),
    ("nine", 9),
];

fn parse_input(input_path: PathBuf) -> std::io::Lines<std::io::BufReader<std::fs::File>> {
    let file: fs::File = fs::File::open(input_path).unwrap();
    let buf: BufReader<fs::File> = std::io::BufReader::new(file);
    buf.lines()
}

fn starts_with_digit(s: &str) -> Option<u32> {
    let first_char: char = s.chars().next().unwrap();

    if first_char.is_numeric() {
        return Some(first_char.to_digit(10).unwrap());
    }

    for (key, value) in WORDS {
        if s.starts_with(key) {
            return Some(value);
        }
    }

    None
}

fn get_digit(s: &String, reverse: bool) -> Option<u32> {
    let range = if !reverse {
        itertools::Either::Left(0..s.len())
    } else {
        itertools::Either::Right((0..=s.len() - 1).rev())
    };
    for i in range {
        match starts_with_digit(&s[i..]) {
            Some(d) => return Some(d),
            None => continue,
        }
    }
    None
}

pub fn solve(path: PathBuf) -> u32 {
    let lines: std::io::Lines<BufReader<fs::File>> = parse_input(path);
    let mut sum = 0;
    for line in lines {
        let l: String = line.unwrap();
        sum += 10 * get_digit(&l, false).unwrap() + get_digit(&l, true).unwrap();
    }
    sum
}