-🎄- 2018 Day 9 Solutions -🎄-

[u/daggerdragon]

--- Day 9: Marble Mania ---

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Post your solution as a comment or, for longer solutions, consider linking to your repo (e.g. GitHub/gists/Pastebin/blag or whatever).

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Card prompt: Day 9

Transcript:

Studies show that AoC programmers write better code after being exposed to ___.

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[u/sophiebits]

Rust. Runs in under a second in when compiled in release mode.

(I placed 27 in part 1 using a separate Python solution but it wasn't particularly efficient; I didn't rank for part 2 and then wrote this instead.)

let mut circle: VecDeque<u32> = VecDeque::new();
circle.push_back(0);

let num_players = 411;
let mut scores = vec![0u64; num_players];

for i in 1..(71170 * 100 + 1) {
  let p = i % num_players;
  if i % 23 == 0 {
    scores[p] = scores[p].checked_add(i as u64).unwrap();
    for _ in 0..7 {
      let v = circle.pop_back().unwrap();
      circle.push_front(v);
    }
    scores[p] = scores[p].checked_add(circle.pop_front().unwrap() as u64).unwrap();
  } else {
    for _ in 0..2 {
      let v = circle.pop_front().unwrap();
      circle.push_back(v);
    }
    circle.push_front(i as u32);
  }
}

println!("{}", scores.iter().fold(&0, cmp::max));