advent-of-code/2023
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day(09): do ‹find_next› in-situ

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Signed-off-by: Matej Focko <mfocko@redhat.com>
This commit is contained in:
Matej Focko 2023-12-09 13:20:31 +01:00
parent 018ee668d4
commit 4a2e0fef55
Signed by: mfocko
GPG key ID: 7C47D46246790496
1 changed files with 12 additions and 10 deletions
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22
src/bin/day09.rs
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@ -8,18 +8,20 @@ struct Day09 {
} }
impl Day09 { impl Day09 {
fn find_next(xs: &[i32]) -> i32 { fn find_next(mut xs: Vec<i32>) -> i32 {
let last = *xs.last().unwrap();
let mut ds = vec![]; let mut ds = vec![];
while xs.iter().any(|&x| x != 0) {
for i in 0..xs.len() - 1 {
xs[i] = xs[i + 1] - xs[i];
}
xs.pop();
let mut last_row = xs.to_owned(); ds.push(*xs.last().unwrap());
while last_row.iter().any(|&x| x != 0) {
let next_row = last_row.windows(2).map(|s| s[1] - s[0]).collect_vec();
ds.push(*next_row.last().unwrap());
last_row = next_row;
} }
xs.last().unwrap() + ds.iter().rev().sum::<i32>() last + ds.iter().rev().sum::<i32>()
} }
} }
@ -34,7 +36,7 @@ impl Solution<Output1, Output2> for Day09 {
} }
fn part_1(&mut self) -> Output1 { fn part_1(&mut self) -> Output1 {
self.values.iter().map(|xs| Self::find_next(xs)).sum() self.values.iter().cloned().map(Self::find_next).sum()
} }
fn part_2(&mut self) -> Output2 { fn part_2(&mut self) -> Output2 {
@ -46,7 +48,7 @@ impl Solution<Output1, Output2> for Day09 {
ys ys
}) })
.map(|xs| Self::find_next(&xs)) .map(Self::find_next)
.sum() .sum()
} }
} }