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2020: day09: optimize using cumulated sum

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This commit is contained in:
Antoine Martin 2020-12-09 08:53:19 +01:00
parent a0611f1fb3
commit 35899f02f9
1 changed files with 15 additions and 10 deletions
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25
aoc2020/src/day09.rs
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@ -54,15 +54,20 @@ fn part1(input: &str) -> aoc::Result<u64> {
Ok(solution) Ok(solution)
} }
fn find_contiguous_range(numbers: &[u64], total: u64, total_idx: usize) -> aoc::Result<(u64, u64)> { fn find_contiguous_range(numbers: &[u64], total: u64) -> aoc::Result<(u64, u64)> {
for i in 0..total_idx { // compute cumulated sums for the whole range
for j in (i + 1)..total_idx { let (sums, _) = numbers.iter().fold((vec![0], 0), |(mut vec, acc), n| {
let range = &numbers[i..=j]; let acc = acc + n;
vec.push(acc);
if range.iter().sum::<u64>() == total { (vec, acc)
// it's safe to unwrap here because j > i so the range always has one number });
let min = range.iter().min().unwrap();
let max = range.iter().max().unwrap(); for i in 0..sums.len() {
for j in (i + 1)..sums.len() {
if sums[j] - sums[i] == total {
let min = numbers[i..j].iter().min().unwrap();
let max = numbers[i..j].iter().max().unwrap();
return Ok((*min, *max)); return Ok((*min, *max));
} }
@ -81,7 +86,7 @@ fn part2(input: &str) -> aoc::Result<u64> {
let (outlier, idx) = find_outlier(&numbers, 25)?; let (outlier, idx) = find_outlier(&numbers, 25)?;
let (min, max) = find_contiguous_range(&numbers, outlier, idx)?; let (min, max) = find_contiguous_range(&numbers[..idx], outlier)?;
Ok(min + max) Ok(min + max)
} }
@ -116,7 +121,7 @@ mod tests {
let (outlier, idx) = find_outlier(&numbers, 5).unwrap(); let (outlier, idx) = find_outlier(&numbers, 5).unwrap();
let (min, max) = find_contiguous_range(&numbers, outlier, idx).unwrap(); let (min, max) = find_contiguous_range(&numbers[..idx], outlier).unwrap();
assert_eq!(min, 15); assert_eq!(min, 15);
assert_eq!(max, 47); assert_eq!(max, 47);