115 lines
3.1 KiB
Rust
115 lines
3.1 KiB
Rust
use aoc_runner_derive::{aoc, aoc_generator};
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type Input = Vec<usize>;
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#[aoc_generator(day9)]
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fn parse(input: &str) -> Input {
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input
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.chars()
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.map(|c| c.to_digit(10).unwrap() as usize)
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.collect()
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}
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#[aoc(day9, part1)]
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fn part1(input: &Input) -> usize {
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let mut sum = 0;
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let mut len = input.chunks(2).map(|c| c[0]).sum::<usize>();
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let mut l_idx = 0;
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let mut l_pos = 0;
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let mut r_idx = input.len() + 1;
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let mut r_left = 0;
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while len > 0 {
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if l_idx % 2 == 0 {
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for _ in 0..input[l_idx] {
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// println!("l {}*{}", l_pos, l_idx / 2);
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// print!("{}", l_idx / 2);
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len -= 1;
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sum += (l_idx / 2) * l_pos;
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l_pos += 1;
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if len == 0 {
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break;
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}
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}
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l_idx += 1;
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} else {
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for _ in 0..input[l_idx] {
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while r_left == 0 {
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r_idx -= 2;
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r_left = input[r_idx];
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}
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// println!("r {}*{}", l_pos, r_idx / 2);
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// print!("{}", r_idx / 2);
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len -= 1;
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sum += (r_idx / 2) * l_pos;
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l_pos += 1;
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r_left -= 1;
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if len == 0 {
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break;
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}
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}
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l_idx += 1;
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}
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}
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sum
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}
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#[aoc(day9, part2)]
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fn part2(input: &Input) -> usize {
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let mut input = input
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.iter()
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.map(|c| (0, *c, *c))
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.collect::<Vec<(usize, usize, usize)>>();
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for i in 1..input.len() {
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input[i].0 = input[i - 1].0 + input[i - 1].1;
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}
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let mut min_idx = [1; 10];
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let mut sum = 0;
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for r_idx in (0..input.len()).step_by(2).rev() {
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let val = r_idx / 2;
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let count = input[r_idx].2;
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for l_idx in (min_idx[count]..r_idx).step_by(2) {
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if input[l_idx].1 >= input[r_idx].2 {
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input[r_idx].0 = input[l_idx].0;
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input[l_idx].1 -= input[r_idx].2;
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input[l_idx].0 += input[r_idx].2;
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input[l_idx - 1].1 += input[r_idx].2;
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for i in count..10 {
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if min_idx[i] > min_idx[count] {
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break;
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} else {
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while min_idx[i] <= r_idx && input[min_idx[i]].1 < i {
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min_idx[i] += 2;
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}
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}
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}
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break;
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}
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}
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sum += val * (count * input[r_idx].0 + count * (count - 1) / 2);
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}
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sum
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn part1_example() {
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assert_eq!(part1(&parse("2333133121414131402")), 1928);
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assert_eq!(
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part1(&parse(include_str!("../input/2024/day9.txt").trim_end())),
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6337921897505
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);
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}
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#[test]
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fn part2_example() {
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assert_eq!(part2(&parse("2333133121414131402")), 2858);
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assert_eq!(
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part2(&parse(include_str!("../input/2024/day9.txt").trim_end())),
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6362722604045
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);
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}
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}
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