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use nom::{
character::complete::{line_ending, one_of},
combinator::map,
multi::{many1, separated_list1},
sequence::pair,
IResult,
};
use std::fs;
fn main() -> Result<(), Box<dyn std::error::Error>> {
let input = fs::read_to_string("inputs/day_13.txt")?;
let parsed = ManyMaps::parser(&input).unwrap().1;
dbg!(&parsed.reflection_score_sum(0));
dbg!(&parsed.reflection_score_sum(1));
Ok(())
}
#[derive(Debug)]
struct ManyMaps(Vec<Map>);
#[derive(Debug)]
struct Map {
rows: Vec<String>,
cols: Vec<String>,
}
impl ManyMaps {
fn parser(input: &str) -> IResult<&str, Self> {
map(
separated_list1(pair(line_ending, line_ending), Map::parser),
ManyMaps,
)(input)
}
fn reflection_score_sum(&self, expected_smudge_count: usize) -> usize {
self.0
.iter()
.map(|m| m.reflection_score(expected_smudge_count))
.sum()
}
}
impl Map {
fn parser(input: &str) -> IResult<&str, Self> {
map(separated_list1(line_ending, many1(one_of(".#"))), |rows| {
Map {
rows: rows
.iter()
.map(|char_array| char_array.iter().collect::<String>())
.collect(),
cols: (0..rows[0].len())
.map(|i| rows.iter().map(|row| row[i]).collect::<String>())
.collect(),
}
})(input)
}
fn reflection_score(&self, expected_smudge_count: usize) -> usize {
reflection_i(&self.cols, expected_smudge_count)
.or_else(|| reflection_i(&self.rows, expected_smudge_count).map(|y| y * 100))
.expect("No reflection!")
}
}
fn reflection_i(rows: &[String], expected_smudge_count: usize) -> Option<usize> {
for i in 1..rows.len() {
let mut smudge_count = 0;
for d in 1..=(i.min(rows.len() - i)) {
smudge_count += rows[i - d]
.chars()
.zip(rows[i + d - 1].chars())
.filter(|(a, b)| a != b)
.count();
}
let is_reflection = smudge_count == expected_smudge_count;
if is_reflection {
return Some(i);
}
}
None
}
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