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day 12 solution

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Andrew Coleman 2018-12-18 17:08:23 -05:00
parent 3f9da45a71
commit 8fedd15dc8
4 changed files with 229 additions and 0 deletions
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95
2018/day12/Cargo.lock generated Normal file
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8
2018/day12/Cargo.toml Normal file
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[package]
name = "day12"
version = "0.1.0"
authors = ["Andrew Coleman <penguincoder@gmail.com>"]
edition = "2018"
[dependencies]
regex = "1"

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initial state: ##.#...#.#.#....###.#.#....##.#...##.##.###..#.##.###..####.#..##..#.##..#.......####.#.#..#....##.#
#.#.# => #
..#.# => .
.#.## => #
.##.. => .
##... => #
##..# => #
#.##. => #
.#..# => #
.#### => .
....# => .
#.... => .
#.### => .
###.# => #
.#.#. => .
#...# => .
.#... => #
##.#. => #
#..## => #
..##. => .
####. => #
.###. => .
##### => .
#.#.. => .
...#. => .
..#.. => .
###.. => #
#..#. => .
.##.# => .
..... => .
##.## => #
..### => #
...## => #

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use std::collections::HashMap;
use std::fs::File;
use std::io::{BufRead, BufReader};
use std::iter::Iterator;
const MAP_SIZE: usize = 500;
const MAP_ZERO_INDEX: usize = 200;
fn get_score(state: &[char; MAP_SIZE]) -> i64 {
let mut score = 0;
for i in 0..MAP_SIZE {
if state[i] == '#' {
score += (i - MAP_ZERO_INDEX) as i64;
}
}
score
}
fn run_game(initial_state: String, states: HashMap<String, char>, generations: i64) -> (i64, [i64; MAP_SIZE]) {
let mut last_state = ['.'; MAP_SIZE];
for (i, c) in initial_state.char_indices() {
if c == '#' {
last_state[MAP_ZERO_INDEX + i] = '#';
}
}
let mut scores = [0i64; MAP_SIZE];
for gen in 0..generations {
let mut next_state = ['.'; MAP_SIZE];
for i in 2..(MAP_SIZE - 2) {
let mut key = String::new();
for j in i-2..=i+2 {
key.push(last_state[j]);
}
if let Some(dest_state) = states.get(&key) {
next_state[i] = *dest_state;
}
}
last_state = next_state;
scores[gen as usize] = get_score(&last_state);
}
(scores[generations as usize - 1], scores)
}
fn find_big_score(initial_state: String, states: HashMap<String, char>, iterations: i64) -> i64 {
let (_, scores) = run_game(initial_state, states, MAP_SIZE as i64);
for i in 0..(MAP_SIZE - 3) {
let diff1 = scores[i + 1] - scores[i];
let diff2 = scores[i + 2] - scores[i + 1];
let diff3 = scores[i + 3] - scores[i + 2];
if diff1 == diff2 {
if diff2 == diff3 {
let sum = ((iterations - i as i64 - 1) * diff1) + scores[i];
println!("({} - {}) * {} + {} = {}", iterations - 1, i as i64, diff1, scores[i], sum);
return sum;
}
}
}
-1
}
fn main() {
let mut lines: Vec<String> = BufReader::new(File::open("input").unwrap())
.lines()
.map(|line| line.unwrap())
.collect();
let mut default_state = lines.remove(0);
default_state.replace_range(0..15, "");
lines.remove(0);
let mut states: HashMap<String, char> = HashMap::new();
for line in lines.iter() {
let mut chars = line.chars();
let mut state = String::with_capacity(5);
state.push(chars.nth(0).unwrap());
state.push(chars.nth(0).unwrap());
state.push(chars.nth(0).unwrap());
state.push(chars.nth(0).unwrap());
state.push(chars.nth(0).unwrap());
let dest = chars.nth(4).unwrap();
states.insert(state, dest);
}
let (part1score, _) = run_game(default_state.clone(), states.clone(), 20);
println!("part 1 score after 20 generations: {}", part1score);
let iterations = 50000000000;
let part2score = find_big_score(default_state, states, iterations);
println!("part 2 score after {} is {}", iterations, part2score);
}