1 files changed, 137 insertions, 0 deletions
diff --git a/2020/src/bin/day_7.rs b/2020/src/bin/day_7.rs
new file mode 100644
index 0000000..45cb9ee
--- /dev/null
+++ b/2020/src/bin/day_7.rs
@@ -0,0 +1,137 @@
+use bevy::prelude::*;
+use std::collections::{BTreeMap, BTreeSet};
+use std::fs::File;
+use std::io::{BufRead, BufReader};
+
+fn main() {
+    App::build()
+        .add_resource(WindowDescriptor {
+            title: "Advent of Code".to_string(),
+            width: 1920,
+            height: 1080,
+            ..Default::default()
+        })
+        .add_resource(ClearColor(Color::rgb(0., 0., 0.)))
+        .add_startup_system(setup_camera.system())
+        .add_startup_system(read_input_file.system())
+        .add_system(trim_empty_bags.system())
+        .add_system(add_known_sizes.system())
+        .add_system(report_gold_bag_known_size.system())
+        //.add_system(debug_print_bags.system())
+        .add_plugins(DefaultPlugins)
+        .run();
+}
+
+fn setup_camera(mut commands: Commands) {
+    commands.spawn(Camera2dComponents::default());
+}
+
+const TARGET_COLOUR: &str = "shiny gold";
+
+struct Bag {
+    colour: String,
+    required: BTreeMap<String, usize>,
+}
+struct CantContainShinyGold;
+#[derive(Clone)]
+struct KnownSize(usize);
+
+fn read_input_file(mut commands: Commands) {
+    let f = File::open("./inputs/day_7.txt").unwrap();
+
+    for line in BufReader::new(f).lines() {
+        let line = line.unwrap();
+        let line = line.trim();
+
+        let (src_colour, contents) = split_2(line, "bags contain");
+        let contents_parts = contents
+            .trim_end_matches('.')
+            .split(',')
+            .filter(|part| part != &"no other bags")
+            .map(|part| {
+                let (quantity, colour) = split_2(
+                    part.trim().trim_end_matches("bags").trim_end_matches("bag"),
+                    " ",
+                );
+                (colour, quantity.parse().unwrap())
+            })
+            .collect();
+        commands.spawn((Bag {
+            colour: src_colour,
+            required: contents_parts,
+        },));
+    }
+}
+
+fn split_2(line: &str, split: &str) -> (String, String) {
+    let parts = line.splitn(2, split).collect::<Vec<_>>();
+    assert_eq!(parts.len(), 2);
+    (parts[0].trim().to_string(), parts[1].trim().to_string())
+}
+
+fn debug_print_bags(bags: Query<&Bag>) {
+    for bag in bags.iter() {
+        println!("{} requires {:?}", bag.colour, bag.required);
+    }
+}
+
+fn trim_empty_bags(
+    mut commands: Commands,
+    bags: Query<Without<CantContainShinyGold, (Entity, &Bag)>>,
+) {
+    let mut colours_cleared = BTreeSet::new();
+    for (entity, bag) in bags.iter() {
+        let required_not_relevant = bag.required.keys().all(|required| {
+            !bags
+                .iter()
+                .any(|can_contain_shiny_gold| &can_contain_shiny_gold.1.colour == required)
+        });
+        if required_not_relevant && bag.colour != TARGET_COLOUR {
+            colours_cleared.insert(bag.colour.clone());
+            commands.insert_one(entity, CantContainShinyGold);
+        }
+    }
+
+    if colours_cleared.is_empty() {
+        println!(
+            "{} bags can hold the shiny gold one",
+            bags.iter().count() - 1
+        );
+    }
+}
+
+fn add_known_sizes(mut commands: Commands, bags: Query<(Entity, &Bag, Option<&KnownSize>)>) {
+    for (entity, bag, size) in bags.iter() {
+        if size.is_some() {
+            continue;
+        }
+
+        let mut new_size = Some(0);
+        for (required_colour, required_quantity) in bag.required.iter() {
+            if new_size.is_none() {
+                break;
+            }
+
+            let inner_bag_size = bags
+                .iter()
+                .find(|(_, bag, _)| &bag.colour == required_colour)
+                .and_then(|(_, _, size)| size.clone());
+            new_size = new_size
+                .zip(inner_bag_size)
+                .map(|(a, b)| a + required_quantity * b.0)
+        }
+
+        if let Some(new_size) = new_size {
+            commands.insert_one(entity, KnownSize(new_size + 1));
+        }
+    }
+}
+
+fn report_gold_bag_known_size(bags: Query<(&Bag, &KnownSize)>) {
+    println!("{} have a known size", bags.iter().count());
+    for (bag, size) in bags.iter() {
+        if bag.colour == TARGET_COLOUR {
+            println!("The shiny gold bag must contain {} other bags!", size.0 - 1)
+        }
+    }
+}