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|
use std::{
error::Error,
fs::File,
io::{BufRead, BufReader},
num::ParseIntError,
};
#[derive(PartialEq, Eq)]
enum Dir {
Ascending,
Descending,
}
impl Dir {
fn characterise(a: i16, b: i16) -> Option<Self> {
let dir = if a < b {
Self::Ascending
} else {
Self::Descending
};
if dir.diff_ok(a, b) {
Some(dir)
} else {
None
}
}
fn diff_ok(&self, a: i16, b: i16) -> bool {
let diff = match *self {
Self::Ascending => b - a,
Self::Descending => a - b,
};
(1..=3).contains(&diff)
}
}
fn p1cond(report: &[i16]) -> bool {
if report.len() <= 1 {
return true;
}
let Some(dir) = Dir::characterise(report[0], report[1]) else {
return false;
};
for win in report[1..].windows(2) {
if !dir.diff_ok(win[0], win[1]) {
return false;
}
}
true
}
fn p2cond(report: &[i16]) -> bool {
if report.len() <= 2 {
// One element can always be removed to make a safe report
return true;
}
'outer: for skip_i in 0..report.len() {
let it =
report
.iter()
.copied()
.enumerate()
.filter_map(|(i, e)| if i != skip_i { Some(e) } else { None });
let mut pairs = it.clone().zip(it.skip(1));
let Some((a, b)) = pairs.next() else {
continue;
};
let Some(dir) = Dir::characterise(a, b) else {
continue;
};
for (a, b) in pairs {
if !dir.diff_ok(a, b) {
continue 'outer;
}
}
return true;
}
false
}
fn main() -> Result<(), Box<dyn Error>> {
let f = File::open("input/2")?;
let f = BufReader::new(f);
let mut input = Vec::new();
for line in f.lines() {
let elems = line?
.trim_end()
.split(' ')
.map(str::parse::<i16>)
.collect::<Result<Vec<_>, ParseIntError>>()?
.into_boxed_slice();
input.push(elems);
}
let input = input.into_boxed_slice();
println!("{}", input.iter().filter(|e| p1cond(e)).count());
println!("{}", input.iter().filter(|e| p2cond(e)).count());
Ok(())
}
|
