62 lines
1.2 KiB
Rust
62 lines
1.2 KiB
Rust
use itertools::Itertools;
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fn main() {
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println!("{}", part2(include_str!("./input.txt")));
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}
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fn part2(input: &str) -> i64 {
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input.lines().map(line).sum()
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}
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fn line(input: &str) -> i64 {
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let nums = input
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.split_ascii_whitespace()
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.map(|s| s.parse::<i64>().expect("invalid digit"))
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.collect::<Vec<_>>();
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find_previous(&nums)
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}
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fn find_previous(line: &[i64]) -> i64 {
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let differences = line
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.iter()
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.tuple_windows::<(_, _)>()
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.map(|(a, b)| b - a)
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.collect::<Vec<_>>();
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let first = *line.first().expect("invalid input");
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if differences.iter().all(|d| *d == 0) {
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first
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} else {
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first - find_previous(&differences)
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}
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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 indoc::indoc;
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#[test]
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fn test_part2() {
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assert_eq!(
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part2(indoc!(
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"
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0 3 6 9 12 15
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1 3 6 10 15 21
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10 13 16 21 30 45
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"
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)),
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2
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);
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}
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#[test]
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fn test_lines_part2() {
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assert_eq!(line("0 3 6 9 12 15"), -3);
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assert_eq!(line("1 3 6 10 15 21"), 0);
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assert_eq!(line("10 13 16 21 30 45"), 5);
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}
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}
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