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static DAY: u8 = 20;
fn main() {
let input = advent::read_lines(DAY);
println!("{DAY}a: {}", grove_coordinates(&input, false));
println!("{DAY}b: {}", grove_coordinates(&input, true));
}
fn grove_coordinates(input: &[String], full_decryption: bool) -> isize {
let (decryption_key, rounds) = if full_decryption { (811589153, 10) } else { (1, 1) };
let mut input = input.iter()
.enumerate()
.map(|(idx,x)| (idx, x.parse::<isize>().unwrap() * decryption_key))
.collect::<Vec<_>>();
for _ in 0 .. rounds {
for idx in 0 .. input.len() {
let pos = input.iter().position(|x| x.0 == idx).unwrap();
let val = input[pos].1;
input.remove(pos);
let input_len = input.len() as isize;
let pos_diff = val % input_len;
let mut new_pos = (pos as isize + pos_diff) % input_len;
if new_pos <= 0 {
new_pos += input_len;
}
input.insert(new_pos as usize, (idx, val));
}
}
let pos = input.iter().position(|x| x.1 == 0).unwrap();
let n = ((pos + 1000) % input.len(), (pos + 2000) % input.len(), (pos + 3000) % input.len());
input[n.0].1 + input[n.1].1 + input[n.2].1
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test() {
let input = [
"1",
"2",
"-3",
"3",
"-2",
"0",
"4",
].iter().map(|&x| String::from(x)).collect::<Vec<_>>();
assert_eq!(grove_coordinates(&input, false), 3);
assert_eq!(grove_coordinates(&input, true), 1623178306);
}
}
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