83 lines
2.1 KiB
Rust
83 lines
2.1 KiB
Rust
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#![feature(test, destructuring_assignment)]
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extern crate test;
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use aoc2020::common::*;
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use itertools::Itertools;
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// Port of the rosetta code Python implementation
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fn chinese_remainder(divs: Vec<i64>, rems: Vec<i64>) -> i64 {
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fn mul_inv(mut a: i64, mut b: i64) -> i64 {
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if b == 1 {
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return 1;
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}
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let (mut x0, mut x1, b0) = (0, 1, b);
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while a > 1 {
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let q = a / b;
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(a, b) = (b, a % b);
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(x0, x1) = (x1 - q * x0, x0);
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}
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if x1 < 0 {
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x1 += b0;
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}
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return x1;
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}
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let mut sum = 0;
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let prod: i64 = divs.iter().product();
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for (div, rem) in divs.iter().zip(rems.iter()) {
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let p = prod / div;
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sum += rem * mul_inv(p, *div) * p;
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}
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return sum % prod;
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}
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type Parsed = (i64, Vec<Option<i64>>);
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fn read_input() -> String {
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read_file(13)
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}
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fn parse_input(raw: &str) -> Parsed {
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let (first, second) = raw.lines().next_tuple().unwrap();
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(first.parse().unwrap(), second.split(',').map(|n| n.parse().ok()).collect())
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}
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fn part1((start, nums): &Parsed) -> i64 {
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let nums = nums.iter().filter_map(|&n| n).collect_vec();
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let (eta, line) = (*start..).find_map(|t| nums.iter().find(|&n| t % n == 0).map(|n| (t, n))).unwrap();
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(eta - start) * line
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}
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fn part2((_, lines): &Parsed) -> i64 {
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let rems = lines.iter().enumerate().filter_map(|(n, l)| l.map(|l| l - n as i64)).collect_vec();
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let lines = lines.iter().filter_map(|&l| l).collect_vec();
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chinese_remainder(lines, rems)
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}
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fn main() {
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let input = parse_input(&read_input());
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println!("Part 1: {}", part1(&input));
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println!("Part 2: {}", part2(&input));
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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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use aoc2020::*;
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use paste::paste;
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use test::black_box;
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const TEST_INPUT: &str = "939
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7,13,x,x,59,x,31,19";
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#[test]
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fn chinese_remainder_test() {
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let divs = vec![3, 5, 7];
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let rems = vec![2, 3, 2];
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assert_eq!(chinese_remainder(divs, rems), 23);
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}
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test!(part1() == 295);
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test!(part2() == 1068781);
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bench!(part1() == 102);
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bench!(part2() == 327300950120029);
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}
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