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day 7 optimizations

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- no need to sort thanks to `select_nth_unstable()`
- don't copy the array around
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swaits committed 2021-12-08 21:09:08 -07:00
1 parent cd0c64b152
commit b283c88975
1 file changed
+14 -14
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src/day07.rs
+14 -14
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@@ -2,10 +2,10 @@ use anyhow::Result;
use crate::utils::parse_by_char; use crate::utils::parse_by_char;
fn get_median(positions: &[isize]) -> isize { fn get_median(positions: &mut [isize]) -> isize {
let mut sorted_pos = positions.to_owned(); let median_index = positions.len() / 2;
sorted_pos.sort_unstable(); positions.select_nth_unstable(median_index); // quickselect in the standard library!
sorted_pos[sorted_pos.len() / 2] positions[median_index]
} }
fn compute_fuel(positions: &[isize], target: isize, cheap_fuel: bool) -> usize { fn compute_fuel(positions: &[isize], target: isize, cheap_fuel: bool) -> usize {
@@ -22,7 +22,7 @@ fn compute_fuel(positions: &[isize], target: isize, cheap_fuel: bool) -> usize {
.sum() .sum()
} }
fn find_cheapest_location(positions: &[isize], cheap_fuel: bool) -> usize { fn find_cheapest_location(positions: &mut [isize], cheap_fuel: bool) -> usize {
// find start point // find start point
let start = get_median(positions); let start = get_median(positions);
let mut position = start; let mut position = start;
@@ -56,10 +56,10 @@ fn find_cheapest_location(positions: &[isize], cheap_fuel: bool) -> usize {
} }
pub(crate) fn run() -> Result<(usize, usize)> { pub(crate) fn run() -> Result<(usize, usize)> {
let data = parse_by_char::<isize>(include_str!("../data/day07.txt"), ',').unwrap(); let mut data = parse_by_char::<isize>(include_str!("../data/day07.txt"), ',').unwrap();
Ok(( Ok((
find_cheapest_location(&data, true), find_cheapest_location(&mut data, true),
find_cheapest_location(&data, false), find_cheapest_location(&mut data, false),
)) ))
} }
@@ -69,15 +69,15 @@ mod tests {
#[test] #[test]
fn test_example() { fn test_example() {
let data = parse_by_char::<isize>(include_str!("../data/day07-test.txt"), ',').unwrap(); let mut data = parse_by_char::<isize>(include_str!("../data/day07-test.txt"), ',').unwrap();
assert_eq!(find_cheapest_location(&data, true), 37); assert_eq!(find_cheapest_location(&mut data, true), 37);
assert_eq!(find_cheapest_location(&data, false), 168); assert_eq!(find_cheapest_location(&mut data, false), 168);
} }
#[test] #[test]
fn test_my_data() { fn test_my_data() {
let data = parse_by_char::<isize>(include_str!("../data/day07.txt"), ',').unwrap(); let mut data = parse_by_char::<isize>(include_str!("../data/day07.txt"), ',').unwrap();
assert_eq!(find_cheapest_location(&data, true), 344138); assert_eq!(find_cheapest_location(&mut data, true), 344138);
assert_eq!(find_cheapest_location(&data, false), 94862124); assert_eq!(find_cheapest_location(&mut data, false), 94862124);
} }
} }