66 lines
1.6 KiB
Rust
66 lines
1.6 KiB
Rust
pub fn run() {
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let input = include_str!("../input/day9.txt");
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// let input = r#"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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let sequences = input.lines().map(parse_sequence).collect::<Vec<_>>();
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dbg!(sequences.iter().map(|s| extrapolate(&s)).sum::<i32>());
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dbg!(sequences.iter().map(|s| extrapolate_back(&s)).sum::<i32>());
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}
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fn parse_sequence(s: &str) -> Vec<i32> {
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s.trim().split(" ").map(|s| s.parse().unwrap()).collect()
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}
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fn extrapolate(seq: &[i32]) -> i32 {
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let deltas = deltas(seq);
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if deltas.iter().all(|x| *x == 0) {
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*seq.last().unwrap()
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} else {
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let next_delta = extrapolate(&deltas);
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*seq.last().unwrap() + next_delta
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}
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}
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fn extrapolate_back(seq: &[i32]) -> i32 {
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let deltas = deltas(seq);
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if deltas.iter().all(|x| *x == 0) {
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seq[0]
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} else {
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let prev_delta = extrapolate_back(&deltas);
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seq[0] - prev_delta
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}
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}
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fn deltas(seq: &[i32]) -> Vec<i32> {
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seq.iter()
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.zip(seq.iter().skip(1))
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.map(|(a, b)| b - a)
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.collect()
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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 test_deltas() {
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assert_eq!(deltas(&[1, 2, 3]), vec![1, 1]);
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assert_eq!(deltas(&[1, 1, 1]), vec![0, 0]);
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}
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#[test]
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fn test_extrapolate() {
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assert_eq!(extrapolate(&[1, 1, 1]), 1);
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assert_eq!(extrapolate(&[1, 2, 3]), 4);
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assert_eq!(extrapolate(&[1, 3, 6]), 10);
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}
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#[test]
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fn test_extrapolate_back() {
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assert_eq!(extrapolate_back(&[10, 13, 16, 21, 30, 45]), 5);
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}
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}
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