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pub fn part1() -> anyhow::Result<i64> {
const WINDOW: usize = 25;
let list = crate::util::read_ints("data/9.txt")?;
for i in 0..(list.len() - WINDOW) {
let set = &list[i..i + WINDOW];
let n = list[i + WINDOW];
if !valid(set, n) {
return Ok(n);
}
}
Err(anyhow::anyhow!("failed to find invalid number"))
}
pub fn part2() -> anyhow::Result<i64> {
const WINDOW: usize = 25;
let list = crate::util::read_ints("data/9.txt")?;
let mut invalid = None;
for i in 0..(list.len() - WINDOW) {
let set = &list[i..i + WINDOW];
let n = list[i + WINDOW];
if !valid(set, n) {
invalid = Some(n);
}
}
if invalid.is_none() {
return Err(anyhow::anyhow!("failed to find invalid number"));
}
let invalid = invalid.unwrap();
for i in 0..list.len() {
for j in i..list.len() {
let seq = &list[i..=j];
if invalid == seq.iter().sum() {
return Ok(seq.iter().copied().min().unwrap()
+ seq.iter().copied().max().unwrap());
}
}
}
Err(anyhow::anyhow!(
"failed to find sequence summing to invalid number"
))
}
fn valid(set: &[i64], n: i64) -> bool {
for i in 0..set.len() {
for j in 0..set.len() {
if i == j {
continue;
}
let i = set[i];
let j = set[j];
if i + j == n {
return true;
}
}
}
false
}
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