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use std::fs;
#[derive(Clone, Debug)]
struct Disc {
pos: usize,
period: usize,
}
fn parse(lines: Vec<&str>) -> Vec<Disc> {
let mut result = Vec::new();
// Add a dummy 0th disc for slightly cleaner code later
result.push(Disc { pos: 0, period: 1 });
for line in lines {
let words: Vec<&str> = line.split_ascii_whitespace().collect();
result.push(Disc {
pos: words[11].trim_end_matches('.').parse().unwrap(),
period: words[3].parse().unwrap(),
});
}
result
}
fn solve_puzzle(discs: &Vec<Disc>) -> usize {
let mut t_start = 0;
'outer: loop {
let mut dt = 1;
while dt < discs.len() {
// Calculate the disc's current position. If 0, the capsule
// can continue, otherwise this `t_start' must be rejected.
if (discs[dt].pos + t_start + dt) % discs[dt].period != 0 {
t_start += 1;
continue 'outer;
}
dt += 1;
}
return t_start;
}
}
fn main() {
// Read disc stats from input text file
let input = fs::read_to_string("input.txt").unwrap();
let lines = input.lines().collect();
let mut discs = parse(lines);
// Part 1 gives 203660 for me
println!("Part 1 solution: {}", solve_puzzle(&discs));
discs.push(Disc { pos: 0, period: 11 });
// Part 2 gives 2408135 for me
println!("Part 2 solution: {}", solve_puzzle(&discs));
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn part1_example1() {
let lines = vec![
"Disc #1 has 5 positions; at time=0, it is at position 4.",
"Disc #2 has 2 positions; at time=0, it is at position 1.",
];
let discs = parse(lines);
assert_eq!(solve_puzzle(&discs), 5);
}
}
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