Added solution to puzzle 2015/day19

2015/day19/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "day19"
+version = "0.1.0"
+edition = "2021"
+
+[[bin]]
+name = "day19"
+path = "day19.rs"

2015/day19/day19.rs

@@ -0,0 +1,142 @@
+//! [Day 19: Medicine for Rudolph](https://adventofcode.com/2015/day/19)
+
+use std::collections::HashSet;
+use std::env;
+use std::fs;
+
+struct Puzzle {
+    medicine_molecule: String,
+    replacements: Vec<(String, String)>,
+}
+
+impl Puzzle {
+    fn new() -> Puzzle {
+        Puzzle {
+            medicine_molecule: String::new(),
+            replacements: Vec::new(),
+        }
+    }
+
+    fn configure(&mut self, filename: &str) {
+        let mut data: Vec<String> = fs::read_to_string(filename)
+            .expect("Failed to read input file")
+            .lines()
+            .map(ToString::to_string)
+            .collect();
+
+        self.medicine_molecule = data.pop().unwrap();
+
+        // Remove empty delimiter
+        data.pop();
+
+        for line in data {
+            // Get the replacement rule
+            let mut replacement: Vec<&str> = line.split(" => ").collect();
+            let to = replacement.pop().unwrap().to_string();
+            let from = replacement.pop().unwrap().to_string();
+            self.replacements.push((from, to));
+        }
+    }
+
+    fn part1(&mut self) -> usize {
+        let mut molecules = HashSet::new();
+
+        for (from, to) in &self.replacements {
+            // Split the molecule on each atom
+            let sub_molecules: Vec<String> = self
+                .medicine_molecule
+                .split_inclusive(from)
+                .map(ToString::to_string)
+                .collect();
+
+            // Apply the replacement rule for each atom found
+            for (i, sub_mol) in sub_molecules.iter().enumerate() {
+                let mut generated_molecule = sub_molecules.clone();
+                let sub_mol = sub_mol.replace(from, to);
+                generated_molecule[i] = sub_mol;
+                molecules.insert(generated_molecule.concat());
+            }
+        }
+        molecules.remove(&self.medicine_molecule);
+
+        molecules.len()
+    }
+
+    /// This resolution works but it's not truly what's asked by the puzzle. We don't know if this
+    /// method yields the lowest count of iterations required to produce the molecule. Finding the
+    /// lowest count of iterations is a way harder puzzle and was probably not meant by the author
+    /// of the puzzle. The puzzle input is probably designed in order for only one answer to rise.
+    fn part2(&mut self) -> usize {
+        let mut iterations = 0_usize;
+
+        // Reduce the medicine molecule to the electron is equivalent to create the medicine molecule from the electron
+        while self.medicine_molecule != "e" {
+            for (from, to) in &self.replacements {
+                // Reverse apply the replacement only once
+                if self.medicine_molecule.find(to) != None {
+                    self.medicine_molecule = self.medicine_molecule.replacen(to, from, 1);
+                    break;
+                }
+            }
+            iterations += 1;
+        }
+
+        iterations
+    }
+}
+
+/// Test from the puzzle description
+#[test]
+fn test1() {
+    let mut puzzle = Puzzle::new();
+    puzzle.configure("test01.txt");
+    assert_eq!(puzzle.part1(), 4);
+}
+
+/// Test from the puzzle description
+#[test]
+fn test2() {
+    let mut puzzle = Puzzle::new();
+    puzzle.configure("test02.txt");
+    assert_eq!(puzzle.part1(), 7);
+}
+
+/// Test from the puzzle description
+#[ignore = "Heuristic made to solve the problem does not work here"]
+#[test]
+fn test3() {
+    let mut puzzle = Puzzle::new();
+    puzzle.configure("test03.txt");
+    assert_eq!(puzzle.part2(), 3);
+}
+
+/// Test from the puzzle description
+#[ignore = "Heuristic made to solve the problem does not work here"]
+#[test]
+fn test4() {
+    let mut puzzle = Puzzle::new();
+    puzzle.configure("test04.txt");
+    assert_eq!(puzzle.part2(), 6);
+}
+
+/// Test from a player's input
+#[test]
+fn test5() {
+    let mut puzzle = Puzzle::new();
+    puzzle.configure("test05.txt");
+    assert_eq!(puzzle.part1(), 518);
+    assert_eq!(puzzle.part2(), 200);
+}
+
+fn main() {
+    let mut puzzle = Puzzle::new();
+
+    let args: Vec<String> = env::args().collect();
+    puzzle.configure(args.get(1).expect("No input file"));
+
+    let result = puzzle.part1();
+    println!("{}", result);
+
+    let result = puzzle.part2();
+    println!("{}", result);
+}

2015/day19/test01.txt

@@ -0,0 +1,5 @@
+H => HO
+H => OH
+O => HH
+
+HOH

2015/day19/test02.txt

@@ -0,0 +1,5 @@
+H => HO
+H => OH
+O => HH
+
+HOHOHO

2015/day19/test03.txt

@@ -0,0 +1,7 @@
+e => H
+e => O
+H => HO
+H => OH
+O => HH
+
+HOH

2015/day19/test04.txt

@@ -0,0 +1,7 @@
+e => H
+e => O
+H => HO
+H => OH
+O => HH
+
+HOHOHO

2015/day19/test05.txt

@@ -0,0 +1,45 @@
+Al => ThF
+Al => ThRnFAr
+B => BCa
+B => TiB
+B => TiRnFAr
+Ca => CaCa
+Ca => PB
+Ca => PRnFAr
+Ca => SiRnFYFAr
+Ca => SiRnMgAr
+Ca => SiTh
+F => CaF
+F => PMg
+F => SiAl
+H => CRnAlAr
+H => CRnFYFYFAr
+H => CRnFYMgAr
+H => CRnMgYFAr
+H => HCa
+H => NRnFYFAr
+H => NRnMgAr
+H => NTh
+H => OB
+H => ORnFAr
+Mg => BF
+Mg => TiMg
+N => CRnFAr
+N => HSi
+O => CRnFYFAr
+O => CRnMgAr
+O => HP
+O => NRnFAr
+O => OTi
+P => CaP
+P => PTi
+P => SiRnFAr
+Si => CaSi
+Th => ThCa
+Ti => BP
+Ti => TiTi
+e => HF
+e => NAl
+e => OMg
+
+CRnSiRnCaPTiMgYCaPTiRnFArSiThFArCaSiThSiThPBCaCaSiRnSiRnTiTiMgArPBCaPMgYPTiRnFArFArCaSiRnBPMgArPRnCaPTiRnFArCaSiThCaCaFArPBCaCaPTiTiRnFArCaSiRnSiAlYSiThRnFArArCaSiRnBFArCaCaSiRnSiThCaCaCaFYCaPTiBCaSiThCaSiThPMgArSiRnCaPBFYCaCaFArCaCaCaCaSiThCaSiRnPRnFArPBSiThPRnFArSiRnMgArCaFYFArCaSiRnSiAlArTiTiTiTiTiTiTiRnPMgArPTiTiTiBSiRnSiAlArTiTiRnPMgArCaFYBPBPTiRnSiRnMgArSiThCaFArCaSiThFArPRnFArCaSiRnTiBSiThSiRnSiAlYCaFArPRnFArSiThCaFArCaCaSiThCaCaCaSiRnPRnCaFArFYPMgArCaPBCaPBSiRnFYPBCaFArCaSiAl

README.md

@@ -88,5 +88,6 @@ Puzzle
 [Day 16: Aunt Sue](https://adventofcode.com/2015/day/16)                             | ⭐⭐  | Rust Python
 [Day 17: No Such Thing as Too Much](https://adventofcode.com/2015/day/17)            | ⭐⭐  | Rust
 [Day 18: Like a GIF For Your Yard](https://adventofcode.com/2015/day/18)             | ⭐⭐  | Rust
+[Day 19: Medicine for Rudolph](https://adventofcode.com/2015/day/19)                 | ⭐⭐  | Rust
 [Day 20: Infinite Elves and Infinite Houses](https://adventofcode.com/2015/day/20)   | ⭐⭐  | Rust
 [Day 25: Let It Snow](https://adventofcode.com/2015/day/25)                          | ⭐    | Rust