1 files changed, 242 insertions, 0 deletions
diff --git a/21/src/main.rs b/21/src/main.rs
new file mode 100644
index 0000000..2f3a791
--- /dev/null
+++ b/21/src/main.rs
@@ -0,0 +1,242 @@
+use advent_lib::prelude::*;
+
+use std::collections::BTreeMap;
+use std::collections::BTreeSet;
+
+#[derive(Clone,Debug)]
+struct Food {
+  ingredients: Vec<String>,
+  allergens: Vec<String>,
+}
+
+
+fn main() -> Result<()> {
+  let mut args = std::env::args();
+  if args.len() != 2 {
+    eprintln!("Usage: advent input");
+  }
+  let _ = args.next();
+  let filename = args.next().unwrap();
+
+  let input = advent_lib::read_lines_file(&filename)?;
+
+  let mut foods: Vec<Food> = Vec::new();
+  let mut ingredients: BTreeSet<String> = BTreeSet::new();
+  let mut allergens: BTreeSet<String> = BTreeSet::new();
+  let mut solved_ingredients: BTreeSet<String> = BTreeSet::new();
+  let mut solved_allergens: BTreeSet<String> = BTreeSet::new();
+
+  for line in &input {
+    let paren_point = line.find('(').unwrap();
+    let (ingredients_input, _) = line.split_at(paren_point - 1);
+    let (_, rest) = line.split_at(paren_point);
+
+    let mut food_ingredients = Vec::new();
+    for word in ingredients_input.split(' ') {
+      food_ingredients.push(word.to_string());
+      ingredients.insert(word.to_string());
+    }
+
+    let mut food_allergens = Vec::new();
+    let mut allergens_iterator = rest.split(' ');
+    let _ = allergens_iterator.next();
+    for word in allergens_iterator {
+      let (stripped_word, _) = word.split_at(word.len() - 1);
+      food_allergens.push(stripped_word.to_string());
+      allergens.insert(stripped_word.to_string());
+    }
+
+    foods.push(Food {
+      ingredients: food_ingredients,
+      allergens: food_allergens,
+    });
+  }
+
+  let mut ingredients_could_have_allergens: BTreeMap<String,BTreeSet<String>> =
+      BTreeMap::new();
+  for food in &foods {
+    for ingredient in &food.ingredients {
+      let mut allergen_set = BTreeSet::new();
+      for allergen in &food.allergens {
+        allergen_set.insert(allergen.clone());
+      }
+
+      match ingredients_could_have_allergens.get(ingredient) {
+        Some(previous_set) => {
+          for allergen in previous_set {
+            allergen_set.insert(allergen.to_string());
+          }
+        },
+        None => { }
+      }
+
+      ingredients_could_have_allergens.insert(ingredient.to_string(), allergen_set);
+    }
+  }
+
+  let mut allergens_could_be_ingredients: BTreeMap<String,BTreeSet<String>> =
+      BTreeMap::new();
+  for food in &foods {
+    for allergen in &food.allergens {
+      let mut ingredient_set = BTreeSet::new();
+      for ingredient in &food.ingredients {
+        ingredient_set.insert(ingredient.clone());
+      }
+
+      match allergens_could_be_ingredients.get(allergen) {
+        Some(previous_set) => {
+          let mut intersected_set = BTreeSet::new();
+          for ingredient in ingredient_set.intersection(previous_set) {
+            intersected_set.insert(ingredient.to_string());
+          }
+          ingredient_set = intersected_set;
+        },
+        None => { }
+      }
+
+      allergens_could_be_ingredients.insert(allergen.to_string(), ingredient_set);
+    }
+  }
+
+  loop {
+    let mut removed_any = false;
+
+    loop {
+      let mut mapping_to_remove: Option<(String,String)> = None;
+      for (allergen, possible_ingredients) in &allergens_could_be_ingredients {
+        if solved_allergens.contains(allergen) {
+          continue;
+        }
+
+        if possible_ingredients.len() == 1 {
+          let allergen = allergen.to_string();
+          let ingredient = possible_ingredients.iter().next().unwrap().to_string();
+
+          solved_ingredients.insert(ingredient.clone());
+          solved_allergens.insert(allergen.clone());
+          mapping_to_remove = Some((allergen, ingredient));
+          removed_any = true;
+          break;
+        }
+      }
+
+      match mapping_to_remove {
+        Some((allergen_to_remove, ingredient_to_remove)) => {
+          for allergen in &allergens {
+            if *allergen == allergen_to_remove {
+              continue;
+            }
+            let mut possible_ingredients =
+                allergens_could_be_ingredients.get(allergen).unwrap().clone();
+            possible_ingredients.remove(&ingredient_to_remove);
+            allergens_could_be_ingredients.insert(
+                allergen.to_string(), possible_ingredients);
+          }
+
+          for ingredient in &ingredients {
+            if *ingredient == ingredient_to_remove {
+              continue;
+            }
+            let mut possible_allergens =
+                ingredients_could_have_allergens.get(ingredient).unwrap().clone();
+            possible_allergens.remove(&allergen_to_remove);
+            ingredients_could_have_allergens.insert(
+                ingredient.to_string(), possible_allergens);
+          }
+        },
+        None => {
+          break;
+        },
+      }
+    }
+
+    loop {
+      let mut mapping_to_remove: Option<(String,String)> = None;
+      for (ingredient, possible_allergens) in &ingredients_could_have_allergens {
+        if solved_ingredients.contains(ingredient) {
+          continue;
+        }
+
+        if possible_allergens.len() == 1 {
+          let ingredient = ingredient.to_string();
+          let allergen = possible_allergens.iter().next().unwrap().to_string();
+
+          solved_ingredients.insert(ingredient.clone());
+          solved_allergens.insert(allergen.clone());
+          mapping_to_remove = Some((ingredient, allergen));
+          removed_any = true;
+          break;
+        }
+      }
+
+      match mapping_to_remove {
+        Some((ingredient_to_remove, allergen_to_remove)) => {
+          for allergen in &allergens {
+            if *allergen == allergen_to_remove {
+              continue;
+            }
+            let mut possible_ingredients =
+                allergens_could_be_ingredients.get(allergen).unwrap().clone();
+            possible_ingredients.remove(&ingredient_to_remove);
+            allergens_could_be_ingredients.insert(
+                allergen.to_string(), possible_ingredients);
+          }
+
+          for ingredient in &ingredients {
+            if *ingredient == ingredient_to_remove {
+              continue;
+            }
+            let mut possible_allergens =
+                ingredients_could_have_allergens.get(ingredient).unwrap().clone();
+            possible_allergens.remove(&allergen_to_remove);
+            ingredients_could_have_allergens.insert(
+                ingredient.to_string(), possible_allergens);
+          }
+        },
+        None => {
+          break;
+        },
+      }
+    }
+
+    if !removed_any {
+      break;
+    }
+  }
+
+  let mut ingredients_without_allergens = BTreeSet::new();
+  for ingredient in &ingredients {
+    let possible_allergens = ingredients_could_have_allergens.get(ingredient).unwrap();
+    if possible_allergens.len() == 0 {
+      ingredients_without_allergens.insert(ingredient.to_string());
+    }
+  }
+
+  let mut appearances = 0;
+  for food in &foods {
+    for ingredient in &food.ingredients {
+      if ingredients_without_allergens.contains(ingredient) {
+        appearances += 1;
+      }
+    }
+  }
+  println!("{}", appearances);
+
+  let mut dangerous_ingredients: Vec<String> = Vec::new();
+  let mut sorted_allergens = Vec::new();
+  for allergen in &allergens {
+    sorted_allergens.push(allergen);
+  }
+  sorted_allergens.sort();
+  for allergen in &sorted_allergens {
+    let ingredients = allergens_could_be_ingredients.get(&allergen.to_string()).unwrap();
+    if ingredients.len() == 1 {
+      dangerous_ingredients.push(ingredients.iter().next().unwrap().to_string());
+    }
+  }
+  let list = dangerous_ingredients.join(",");
+  println!("{}", list);
+
+  Ok(())
+}
+