Day 13: Point of Incidence

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  • Deebster
    3·
    1 year ago

    I decided to use string comparison for some reason, which meant part two wasn’t as quick as it would have been.

    use std::{cmp, fs, iter};

fn transpose(rows: &[&str]) -> Vec {
    (0..rows[0].len())
        .map(|i| {
            let bytes: Vec<_> = (0..rows.len()).map(|j| rows[j].as_bytes()[i]).collect();
            String::from_utf8(bytes).unwrap()
        })
        .collect()
}

fn reflection_value(rows: &[&str]) -> Option {
    'row_loop: for i in 0..(rows.len() - 1) {
        if rows[i] != rows[i + 1] {
            continue;
        }
        // we have an initial match
        let other_matches = cmp::min(i, rows.len() - 2 - i);
        for j in 1..=other_matches {
            if rows[i - j] != rows[i + 1 + j] {
                continue 'row_loop;
            }
        }
        return Some(i as u32 + 1);
    }
    None
}

fn summary(file_path: &str) -> u32 {
    fs::read_to_string(file_path)
        .expect("Can't read input file")
        .split("\n\n")
        .map(|s| {
            let rows: Vec<&str> = s.split('\n').collect();

            if let Some(v) = reflection_value(&rows) {
                v * 100
            } else {
                let cols_owned: Vec = transpose(&rows);
                let cols: Vec<&str> = cols_owned.iter().map(|s| s.as_str()).collect();
                reflection_value(&cols).expect("No reflections found")
            }
        })
        .sum()
}

fn str_diff(str1: &str, str2: &str) -> u32 {
    iter::zip(str1.chars(), str2.chars())
        .map(|(s1, s2)| if s1 == s2 { 0 } else { 1 })
        .sum()
}

fn smudged_reflection_value(rows: &[&str]) -> Option {
    for i in 0..(rows.len() - 1) {
        let num_cmps = cmp::min(i, rows.len() - 2 - i);
        let errs: u32 = (0..=num_cmps)
            .map(|j| str_diff(rows[i - j], rows[i + 1 + j]))
            .sum();

        if errs != 1 {
            continue;
        }
        return Some(i as u32 + 1);
    }
    None
}

fn smudged_summary(file_path: &str) -> u32 {
    fs::read_to_string(file_path)
        .expect("Can't read input file")
        .split("\n\n")
        .map(|s| {
            let rows: Vec<&str> = s.split('\n').collect();

            if let Some(v) = smudged_reflection_value(&rows) {
                v * 100
            } else {
                let cols_owned: Vec = transpose(&rows);
                let cols: Vec<&str> = cols_owned.iter().map(|s| s.as_str()).collect();
                smudged_reflection_value(&cols).expect("No reflections found")
            }
        })
        .sum()
}

fn main() {
    println!(" normal: {}", summary("d13/input.txt"));
    println!("smudged: {}", smudged_summary("d13/input.txt"));
}