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static DAY: u8 = 9;
fn main() {
let input = advent::read_lines(DAY);
println!("{DAY}a: {}", sum_extrapolations(&input, false));
println!("{DAY}b: {}", sum_extrapolations(&input, true));
}
fn extrapolate(input: &[i32], previous: bool) -> i32 {
if input.iter().all(|&n| n == 0) {
/* all zeroes */
return 0;
}
let diffs = input.iter()
.as_slice()
.windows(2)
.map(|x| x[1] - x[0])
.collect::<Vec<_>>();
if previous {
input.first().unwrap() - extrapolate(&diffs, previous)
} else {
input.last().unwrap() + extrapolate(&diffs, previous)
}
}
fn sum_extrapolations(input: &[String], previous: bool) -> i32 {
input.iter()
.map(|x| x.split(' ').map(|n| n.parse().unwrap()).collect::<Vec<_>>())
.map(|numbers| extrapolate(&numbers, previous))
.sum()
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test() {
let input = [
"0 3 6 9 12 15",
"1 3 6 10 15 21",
"10 13 16 21 30 45",
].iter().map(|&x| String::from(x)).collect::<Vec<_>>();
assert_eq!(sum_extrapolations(&input, false), 114);
assert_eq!(sum_extrapolations(&input, true), 2);
}
}
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