49 lines
1.2 KiB
Rust
49 lines
1.2 KiB
Rust
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use anyhow::{Context, Result};
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fn extrapolate(sequence: &mut Vec<i64>) -> Option<(i64, i64)> {
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let diff = |seq: &mut Vec<i64>| {
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(0..seq.len() - 1).for_each(|i| seq[i] = seq[i + 1] - seq[i]);
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seq.pop();
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};
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let mut fwd = 0;
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let mut bwd = 0;
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let mut f = 1;
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while sequence.len() > 1 {
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fwd += sequence[sequence.len() - 1];
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bwd += f * sequence[0];
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diff(sequence);
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f *= -1;
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if sequence.iter().all(|&num| num == 0) {
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return Some((bwd, fwd));
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}
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}
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None
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}
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fn main() -> Result<()> {
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let filename = std::env::args()
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.nth(1)
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.context("./day09 <path to puzzle input>")?;
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let input = std::fs::read_to_string(filename)?;
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let mut part1 = 0;
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let mut part2 = 0;
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for line in input.lines() {
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let parse_i64 = |str: &str| str.parse::<i64>().unwrap();
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let mut initial: Vec<i64> = line.split_ascii_whitespace().map(parse_i64).collect();
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let (p2, p1) = extrapolate(&mut initial).context("malformed input")?;
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part1 += p1;
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part2 += p2;
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}
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println!("1) {}", part1);
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println!("2) {}", part2);
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Ok(())
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}
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