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|
pub fn parse(
fh: std::fs::File,
) -> anyhow::Result<impl Iterator<Item = String>> {
Ok(crate::util::parse::lines(fh))
}
pub fn part1(lines: impl Iterator<Item = String>) -> anyhow::Result<i64> {
let (total_lines, by_pos) = pos_counts(lines)?;
let gamma: String = by_pos
.iter()
.map(|pos| if pos * 2 >= total_lines { '1' } else { '0' })
.collect();
let epsilon: String = by_pos
.iter()
.map(|pos| if pos * 2 >= total_lines { '0' } else { '1' })
.collect();
Ok(bin_str_to_int(&gamma) * bin_str_to_int(&epsilon))
}
pub fn part2(lines: impl Iterator<Item = String>) -> anyhow::Result<i64> {
let mut oxygen: Vec<_> = lines.collect();
for i in 0..oxygen[0].len() {
if oxygen.len() == 1 {
break;
}
let (total_lines, by_pos) = pos_counts(oxygen.iter().cloned())?;
let keep = if by_pos[i] * 2 >= total_lines {
'1'
} else {
'0'
};
let new_oxygen = oxygen
.iter()
.filter(|l| l.chars().nth(i).unwrap() == keep)
.cloned()
.collect();
oxygen = new_oxygen;
}
let mut co2: Vec<_> = data_lines!()?.collect();
for i in 0..co2[0].len() {
if co2.len() == 1 {
break;
}
let (total_lines, by_pos) = pos_counts(co2.iter().cloned())?;
let keep = if by_pos[i] * 2 >= total_lines {
'0'
} else {
'1'
};
let new_co2 = co2
.iter()
.filter(|l| l.chars().nth(i).unwrap() == keep)
.cloned()
.collect();
co2 = new_co2;
}
Ok(bin_str_to_int(&oxygen[0]) * bin_str_to_int(&co2[0]))
}
fn pos_counts(
lines: impl std::iter::Iterator<Item = String>,
) -> anyhow::Result<(i64, Vec<i64>)> {
let mut by_pos = vec![];
let mut total_lines = 0;
for line in lines {
total_lines += 1;
if by_pos.is_empty() {
by_pos.resize(line.len(), 0);
}
for (i, c) in line.chars().enumerate() {
if c == '1' {
by_pos[i] += 1;
}
}
}
Ok((total_lines, by_pos))
}
fn bin_str_to_int(s: &str) -> i64 {
let mut ret = 0;
for (i, c) in s.chars().rev().enumerate() {
if c == '1' {
ret += 2i64.pow(i.try_into().unwrap());
}
}
ret
}
#[test]
fn test() {
assert_eq!(
part1(parse(crate::util::data(2021, 3).unwrap()).unwrap()).unwrap(),
3009600
);
assert_eq!(
part2(parse(crate::util::data(2021, 3).unwrap()).unwrap()).unwrap(),
6940518
);
}
|
