Day 3: Gear Ratios


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  • capitalpb@programming.dev
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    11 months ago

    Another day of the 2023 Advent of Code, and another day where I hate looking at my code. This year just seems like it is starting off a lot more complex than I remember in previous years. This one was a little tricky, but I got there without any major setbacks. Another one I am excited to come back to and clean up, but this first pass is all about getting a solution, and this one works.

    https://github.com/capitalpb/advent_of_code_2023/blob/main/src/solvers/day03.rs

    #[derive(Clone, Copy, Debug)]
    struct Location {
        row: usize,
        start_col: usize,
        end_col: usize,
    }
    
    #[derive(Debug)]
    struct EngineSchematic {
        schematic: Vec>,
        numbers: Vec,
        symbols: Vec,
    }
    
    impl EngineSchematic {
        fn from(input: &str) -> EngineSchematic {
            let schematic: Vec> = input.lines().map(|line| line.chars().collect()).collect();
            let mut numbers = vec![];
            let mut symbols = vec![];
            let mut location: Option = None;
    
            for (row_index, row) in schematic.iter().enumerate() {
                for (col, ch) in row.iter().enumerate() {
                    match ch {
                        ch if ch.is_ascii_punctuation() => {
                            if let Some(location) = location {
                                numbers.push(location);
                            }
                            location = None;
    
                            if ch != &'.' {
                                symbols.push(Location {
                                    row: row_index,
                                    start_col: col,
                                    end_col: col,
                                });
                            }
                        }
                        ch if ch.is_digit(10) => {
                            if let Some(mut_location) = location.as_mut() {
                                mut_location.end_col = col;
                            } else {
                                location = Some(Location {
                                    row: row_index,
                                    start_col: col,
                                    end_col: col,
                                });
                            }
                        }
                        _ => {
                            unreachable!("malformed input");
                        }
                    }
                }
    
                if let Some(location) = location {
                    numbers.push(location);
                }
                location = None;
            }
    
            EngineSchematic {
                schematic,
                numbers,
                symbols,
            }
        }
    
        fn get_number_value(&self, location: &Location) -> u32 {
            self.schematic[location.row][location.start_col..=location.end_col]
                .iter()
                .collect::()
                .parse::()
                .unwrap()
        }
    
        fn is_gear(&self, location: &Location) -> bool {
            self.schematic[location.row][location.start_col] == '*'
        }
    
        fn are_adjacent(&self, location: &Location, other_location: &Location) -> bool {
            location.start_col >= other_location.start_col.checked_sub(1).unwrap_or(0)
                && location.end_col <= other_location.end_col + 1
                && (location.row == other_location.row
                    || location.row == other_location.row.checked_sub(1).unwrap_or(0)
                    || location.row == other_location.row + 1)
        }
    }
    
    pub struct Day03;
    
    impl Solver for Day03 {
        fn star_one(&self, input: &str) -> String {
            let schematic = EngineSchematic::from(input);
    
            schematic
                .numbers
                .iter()
                .filter(|number| {
                    schematic
                        .symbols
                        .iter()
                        .any(|symbol| schematic.are_adjacent(symbol, number))
                })
                .map(|number| schematic.get_number_value(number))
                .sum::()
                .to_string()
        }
    
        fn star_two(&self, input: &str) -> String {
            let schematic = EngineSchematic::from(input);
    
            schematic
                .symbols
                .iter()
                .filter(|symbol| schematic.is_gear(symbol))
                .map(|symbol| {
                    let adjacent_numbers = schematic
                        .numbers
                        .iter()
                        .filter(|number| schematic.are_adjacent(symbol, number))
                        .collect::>();
                    if adjacent_numbers.len() == 2 {
                        schematic.get_number_value(adjacent_numbers[0])
                            * schematic.get_number_value(adjacent_numbers[1])
                    } else {
                        0
                    }
                })
                .sum::()
                .to_string()
        }
    }