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|
use nom::{
branch::alt,
character::complete::{char, line_ending, space1, u32},
combinator::{map, value},
multi::{many1, separated_list1},
sequence::separated_pair,
IResult,
};
use std::fs;
fn main() -> Result<(), Box<dyn std::error::Error>> {
let input = fs::read_to_string("inputs/day_12.txt")?;
let small = SpringField::parser(&input).unwrap().1;
dbg!(&small.possibilities_sum());
let large = small.expand();
dbg!(&large.possibilities_sum());
Ok(())
}
#[derive(Debug)]
struct SpringField(Vec<SpringRow>);
#[derive(Debug)]
struct SpringRow {
springs: Vec<Option<Spring>>,
check: Vec<u32>,
}
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
enum Spring {
Good,
Bad,
}
impl SpringField {
fn parser(input: &str) -> IResult<&str, Self> {
map(separated_list1(line_ending, SpringRow::parser), SpringField)(input)
}
fn possibilities_sum(&self) -> usize {
self.0.iter().map(|r| r.possibilities_count()).sum()
}
fn expand(&self) -> SpringField {
SpringField(self.0.iter().map(|r| r.expand()).collect())
}
}
impl SpringRow {
fn parser(input: &str) -> IResult<&str, Self> {
map(
separated_pair(
many1(Spring::parser),
space1,
separated_list1(char(','), u32),
),
|(springs, check)| SpringRow { springs, check },
)(input)
}
fn expand(&self) -> SpringRow {
let mut expanded = SpringRow {
springs: Vec::new(),
check: Vec::new(),
};
for _ in 0..5 {
expanded.springs.append(&mut self.springs.clone());
expanded.springs.push(None);
expanded.check.append(&mut self.check.clone());
}
// should only have the extra None between, not at the very end.
expanded.springs.pop();
expanded
}
fn validate_check(&self, springs: &[Spring]) -> bool {
let mut current_check_index = 0;
let mut current_count = 0;
let mut in_bad_lands = false;
for spring in springs {
match spring {
Spring::Good => {
if in_bad_lands {
let valid = self
.check
.get(current_check_index)
.map_or(false, |expected| *expected == current_count);
if !valid {
return false;
}
current_count = 0;
current_check_index += 1;
}
in_bad_lands = false;
}
Spring::Bad => {
current_count += 1;
in_bad_lands = true;
}
}
}
if in_bad_lands {
let valid = self
.check
.get(current_check_index)
.map_or(false, |expected| *expected == current_count);
if !valid {
return false;
}
current_check_index += 1;
}
self.check.len() == current_check_index
}
fn possibilities_count(&self) -> usize {
let unknown_indexes: Vec<usize> = self
.springs
.iter()
.enumerate()
.filter_map(|(i, s)| s.is_none().then_some(i))
.collect();
assert_ne!(unknown_indexes.len(), 0);
let max_possibilities = 2_usize.pow(unknown_indexes.len().try_into().unwrap());
let mut spring_guess: Vec<Spring> = self
.springs
.iter()
.map(|s| s.unwrap_or(Spring::Bad))
.collect();
let unknown_indexes: Vec<usize> = self
.springs
.iter()
.enumerate()
.filter_map(|(i, s)| s.is_none().then_some(i))
.collect();
let possibilities = (0..max_possibilities)
.filter(|i| {
for (bit_index, spring_index) in unknown_indexes.iter().enumerate() {
spring_guess[*spring_index] = if i & (1 << bit_index) != 0 {
Spring::Bad
} else {
Spring::Good
};
}
self.validate_check(&spring_guess)
})
.count();
possibilities
}
}
impl Spring {
fn parser(input: &str) -> IResult<&str, Option<Self>> {
alt((
value(Some(Spring::Good), char('.')),
value(Some(Spring::Bad), char('#')),
value(None, char('?')),
))(input)
}
}
|
