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