1 files changed, 55 insertions, 0 deletions

diff --git a/day14/src/main.rs b/day14/src/main.rs
new file mode 100644
index 0000000..6cca304
--- /dev/null
+++ b/day14/src/main.rs
@@ -0,0 +1,55 @@
+use std::fs;
+use std::path::Path;
+use std::collections::HashMap;
+use std::iter::FromIterator;
+
+type Expand = (char,char);
+type Rules = HashMap<(char,char),char>;
+type Frequency = HashMap<char,u128>;
+type FrequencyMap = HashMap<Expand,Frequency>;
+
+/* AOC21 Day 14: https://adventofcode.com/2021/day/14 */
+fn main() {
+    let input = Path::new("resources").join("input.txt");
+    let content = fs::read_to_string(input).expect("Unable to read input file");
+    let (template,rules) = content.split_once("\n\n").expect("Malformed input");
+    let rules = Rules::from_iter(rules.lines().map(|l| {
+        let (from,to) = l.split_once(" -> ").expect("Malformed input");
+        let chars = from.chars().collect::<Vec<char>>();
+        ((chars[0],chars[1]),to.parse().unwrap())
+    }));
+    let mut frequency = FrequencyMap::new();
+    rules.iter().for_each(|(&(a,b),&c)| {
+        let mut map = HashMap::new(); map.insert(c,1);
+        frequency.insert((a,b),map);
+    });
+    (1..10).for_each(|_| frequency = expand(&frequency, &rules));
+    println!("Ex1: the result is {}", template_frequency(template, &frequency));
+    (0..30).for_each(|_| frequency = expand(&frequency, &rules));
+    println!("Ex2: the result is {}", template_frequency(template, &frequency));
+}
+
+fn expand(frequency: &FrequencyMap, rules: &Rules) -> FrequencyMap {
+    let mut freq2 = FrequencyMap::new();
+    rules.iter().for_each(|(&(a,b),&c)| {
+        let mut map = merge(frequency.get(&(a,c)).unwrap(), frequency.get(&(c,b)).unwrap());
+        *map.entry(c).or_default() += 1;
+        *freq2.entry((a,b)).or_default() = map;
+    });
+    freq2
+}
+
+fn template_frequency(template: &str, frequency: &FrequencyMap) -> u128 {
+    let mut freq = HashMap::new();
+    template.chars().for_each(|c| *freq.entry(c).or_default() += 1);
+    freq = template.chars().collect::<Vec<char>>()
+                   .as_slice().windows(2)
+                   .fold(freq, |acc, w| merge(&acc, frequency.get(&(w[0],w[1])).unwrap()) );
+    freq.values().max().unwrap() - freq.values().min().unwrap()
+}
+
+fn merge(a: &Frequency, b: &Frequency) -> Frequency {
+    let mut map = a.clone();
+    b.iter().for_each(|(&k,&v)| *map.entry(k).or_default() += v);
+    map
+}