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#![feature(iter_map_windows)]
use std::collections::BTreeSet;
static INPUT: &[u8] = include_bytes!("input.txt");
#[derive(Copy, Clone, Debug)]
enum LineMaskEntry {
Empty,
Gear,
Number{tag: u32, num: u32}
}
fn main() {
let valueified = INPUT.split(|b| *b == b'\n').filter(|s| !s.is_empty());
let mut num = 0;
let (parts_number_sum, gears_mask) = [valueified.clone().next().unwrap()].into_iter().chain(valueified.clone()).chain([valueified.clone().last().unwrap()])
.map_windows::<_, _, 3>(|[prev, curr, next]| {
let mut numlen = 0;
let mut numval = 0;
let mut acc = 0;
let mut linemask = vec![LineMaskEntry::Empty; curr.len()];
for i in 0..curr.len() {
if curr[i] == b'*' { linemask[i] = LineMaskEntry::Gear; }
if !curr[i].is_ascii_digit() && numlen != 0 {
let start = if i - numlen == 0 { i - numlen } else { i - numlen - 1 };
let end = i;
let window = || start..=end;
if prev[window()].into_iter().chain(&curr[window()]).chain(&next[window()]).any(|b| !b.is_ascii_digit() && *b != b'.') {
acc += numval;
linemask[i - numlen .. i].fill(LineMaskEntry::Number{ tag: num, num: numval });
num += 1;
}
numlen = 0;
numval = 0;
}
else if curr[i].is_ascii_digit() {
numlen += 1;
numval *= 10;
numval += (curr[i] - b'0') as u32;
}
}
if numlen != 0 {
let window = || curr.len() - numlen - 1..curr.len();
if prev[window()].into_iter().chain(&curr[window()]).chain(&next[window()]).any(|b| !b.is_ascii_digit() && *b != b'.') {
acc += numval;
linemask[curr.len() - numlen .. curr.len()].fill(LineMaskEntry::Number{ tag: num, num: numval });
num += 1;
}
}
(acc, linemask)
}).fold((0, Vec::new()), |(n, mut v), (a, l)| (n + a, {v.push(l); v}));
println!("Sum of valid part numbers: {parts_number_sum}");
let first = vec![LineMaskEntry::Empty; gears_mask[0].len()];
let last = first.clone();
let gear_ratio_sum = [first].into_iter().chain(gears_mask).chain([last])
.map_windows::<_, _, 3>(|[prev, curr, next]| {
let mut acc = 0;
for i in 0..curr.len() {
match curr[i] {
LineMaskEntry::Gear => {
let mut set = BTreeSet::new();
for row in [prev, curr, next] {
for n in [i - 1, i, i + 1] {
if n == 0 || n == row.len() { continue; }
if let LineMaskEntry::Number{tag, num} = row[n] {
set.insert((tag, num));
}
}
}
if set.len() == 2 {
let mut iter = set.into_iter();
let x = iter.next().unwrap().1;
let y = iter.next().unwrap().1;
acc += x * y
}
},
_ => ()
}
}
acc
}).sum::<u32>();
println!("Gear ratio sum: {gear_ratio_sum}");
}
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