day 12 solution

2018/day12/Cargo.lock

@@ -0,0 +1,95 @@
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+
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+
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+version = "0.1.0"
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+]
+
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+name = "lazy_static"
+version = "1.2.0"
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+
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+]
+
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2018/day12/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "day12"
+version = "0.1.0"
+authors = ["Andrew Coleman <penguincoder@gmail.com>"]
+edition = "2018"
+
+[dependencies]
+regex = "1"

2018/day12/input

@@ -0,0 +1,34 @@
+initial state: ##.#...#.#.#....###.#.#....##.#...##.##.###..#.##.###..####.#..##..#.##..#.......####.#.#..#....##.#
+
+#.#.# => #
+..#.# => .
+.#.## => #
+.##.. => .
+##... => #
+##..# => #
+#.##. => #
+.#..# => #
+.#### => .
+....# => .
+#.... => .
+#.### => .
+###.# => #
+.#.#. => .
+#...# => .
+.#... => #
+##.#. => #
+#..## => #
+..##. => .
+####. => #
+.###. => .
+##### => .
+#.#.. => .
+...#. => .
+..#.. => .
+###.. => #
+#..#. => .
+.##.# => .
+..... => .
+##.## => #
+..### => #
+...## => #

2018/day12/src/main.rs

@@ -0,0 +1,92 @@
+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);
+}