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Remove most allocations from the code path

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Bert Peters
2023-12-09 19:42:20 +01:00
parent 92c985cbd4
commit ee2ff35609
1 changed files with 36 additions and 24 deletions
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60
2023/src/day09.rs
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@@ -1,26 +1,36 @@
use std::mem; use std::mem;
use std::ops::Range;
use nom::bytes::complete::tag;
use nom::multi::many1;
use nom::multi::separated_list1;
use nom::sequence::terminated;
use nom::IResult; use nom::IResult;
use crate::common::parse_input; use crate::common::parse_input;
fn parse_reports(i: &[u8]) -> IResult<&[u8], Vec<Vec<i32>>> { fn parse_reports(mut i: &[u8]) -> IResult<&[u8], (Vec<Range<usize>>, Vec<i32>)> {
many1(terminated( let mut begin = 0;
separated_list1(tag(" "), nom::character::complete::i32), let mut numbers = Vec::new();
tag("\n"), let mut ranges = Vec::new();
))(i) while !i.is_empty() {
let (rem, num) = nom::character::complete::i32(i)?;
numbers.push(num);
if rem[0] == b'\n' {
let end = numbers.len();
ranges.push(begin..end);
begin = end;
}
i = &rem[1..];
}
Ok((i, (ranges, numbers)))
} }
fn compute_next<'a>(report: impl IntoIterator<Item = &'a i32>) -> i32 { fn compute_next<'a>(report: impl IntoIterator<Item = &'a i32>, deltas: &mut Vec<i32>) -> i32 {
let mut deltas = Vec::new(); deltas.clear();
for &entry in report { for &entry in report {
let mut delta = entry; let mut delta = entry;
for prev_delta in &mut deltas { for prev_delta in &mut *deltas {
let prev = mem::replace(prev_delta, delta); let prev = mem::replace(prev_delta, delta);
delta = delta - prev; delta = delta - prev;
} }
@@ -30,23 +40,25 @@ fn compute_next<'a>(report: impl IntoIterator<Item = &'a i32>) -> i32 {
} }
} }
deltas.drain(..).rev().fold(0, |c, d| c + d) deltas.iter().rev().fold(0, |c, d| c + d)
} }
pub fn part1(input: &[u8]) -> anyhow::Result<String> { pub fn part1(input: &[u8]) -> anyhow::Result<String> {
let reports = parse_input(input, parse_reports)?; let mut deltas = Vec::new();
let result: i32 = reports let (ranges, numbers) = parse_input(input, parse_reports)?;
.iter() let result: i32 = ranges
.map(|report| compute_next(report.iter())) .into_iter()
.map(|range| compute_next(&numbers[range], &mut deltas))
.sum(); .sum();
Ok(result.to_string()) Ok(result.to_string())
} }
pub fn part2(input: &[u8]) -> anyhow::Result<String> { pub fn part2(input: &[u8]) -> anyhow::Result<String> {
let mut reports = parse_input(input, parse_reports)?; let mut deltas = Vec::new();
let result: i32 = reports let (ranges, numbers) = parse_input(input, parse_reports)?;
.iter_mut() let result: i32 = ranges
.map(|report| compute_next(report.iter().rev())) .into_iter()
.map(|range| compute_next(numbers[range].iter().rev(), &mut deltas))
.sum(); .sum();
Ok(result.to_string()) Ok(result.to_string())
} }
@@ -59,9 +71,9 @@ mod tests {
#[test] #[test]
fn samples_separate() { fn samples_separate() {
assert_eq!(18, compute_next(&[0, 3, 6, 9, 12, 15])); assert_eq!(18, compute_next(&[0, 3, 6, 9, 12, 15], &mut Vec::new()));
assert_eq!(28, compute_next(&[1, 3, 6, 10, 15, 21])); assert_eq!(28, compute_next(&[1, 3, 6, 10, 15, 21], &mut Vec::new()));
assert_eq!(68, compute_next(&[10, 13, 16, 21, 30, 45])); assert_eq!(68, compute_next(&[10, 13, 16, 21, 30, 45], &mut Vec::new()));
} }
#[test] #[test]