Fast recusive version of day 14

src/bin/day14.rs

@@ -4,6 +4,72 @@ use std::fs::File;
 use std::io::{self, BufRead};
 use std::vec::Vec;
 
+fn recurse_pair(
+    a: char,
+    b: char,
+    depth: usize,
+    rules: &HashMap<(char, char), char>,
+    cache: &mut HashMap<(char, char, usize), HashMap<char, usize>>,
+) -> HashMap<char, usize> {
+    if cache.contains_key(&(a, b, depth)) {
+        return cache[&(a, b, depth)].clone();
+    }
+
+    let middle = rules.get(&(a, b)).unwrap();
+
+    let mut res = HashMap::new();
+    res.insert(*middle, 1);
+
+    if depth == 1 {
+        return res;
+    }
+
+    let res1 = recurse_pair(a, *middle, depth - 1, rules, cache);
+    let res2 = recurse_pair(*middle, b, depth - 1, rules, cache);
+
+    for (c, count) in res1.iter() {
+        let count2 = res.get(c).unwrap_or_else(|| &0).clone();
+        res.insert(*c, count + count2);
+    }
+
+    for (c, count) in res2.iter() {
+        let count2 = res.get(c).unwrap_or_else(|| &0).clone();
+        res.insert(*c, count + count2);
+    }
+
+    cache.insert((a, b, depth), res.clone());
+
+    res
+}
+
+fn compute_dist(
+    polymer_template: &Vec<char>,
+    depth: usize,
+    rules: &HashMap<(char, char), char>,
+    cache: &mut HashMap<(char, char, usize), HashMap<char, usize>>,
+) -> usize {
+    let mut dist: HashMap<char, usize> = HashMap::new();
+    for c in polymer_template.iter() {
+        let count = dist.get(c).unwrap_or_else(|| &0).clone();
+        dist.insert(*c, count + 1);
+    }
+
+    for pair in polymer_template.windows(2) {
+        let res = recurse_pair(pair[0], pair[1], depth, &rules, cache);
+        for (c, count) in res.iter() {
+            let count2 = dist.get(c).unwrap_or_else(|| &0).clone();
+            dist.insert(*c, count + count2);
+        }
+    }
+
+    println!("{:?}", dist);
+
+    let mut counts: Vec<&usize> = dist.values().collect();
+    counts.sort();
+
+    *counts.last().unwrap() - *counts.first().unwrap()
+}
+
 fn main() -> Result<(), Box<dyn Error>> {
     let file = File::open("inputs/day14.txt")?;
     let mut lines = io::BufReader::new(file).lines();
@@ -27,37 +93,15 @@ fn main() -> Result<(), Box<dyn Error>> {
         );
     }
 
-    for i in 0..40 {
-        let mut next_step: Vec<char> = Vec::new();
-        next_step.push(polymer_template[0]);
-        for pair in polymer_template.windows(2) {
-            //next_step.push(pair[0]);
-            if rules.contains_key(&(pair[0], pair[1])) {
-                next_step.push(rules[&(pair[0], pair[1])]);
-            }
-            next_step.push(pair[1]);
-        }
+    let mut cache: HashMap<(char, char, usize), HashMap<char, usize>> = HashMap::new();
 
-        polymer_template = next_step;
+    let answer1 = compute_dist(&polymer_template, 10, &rules, &mut cache);
 
-        println!("{} : {}", i, polymer_template.len());
-    }
+    println!("Answer1: {}", answer1);
 
-    let mut dist: HashMap<char, usize> = HashMap::new();
-    for c in polymer_template.iter() {
-        let count = dist.get(c).unwrap_or_else(|| &0).clone();
-        dist.insert(*c, count + 1);
-    }
+    let answer2 = compute_dist(&polymer_template, 40, &rules, &mut cache);
 
-    let mut counts: Vec<&usize> = dist.values().collect();
-    counts.sort();
-
-    println!(
-        "Answer1: {}",
-        *counts.last().unwrap() - *counts.first().unwrap()
-    );
-
-    println!("Answer2: {}", 0);
+    println!("Answer2: {}", answer2);
 
     Ok(())
 }