From 02973bde28a8a23d2657accda9b76bf9b6ebf61c Mon Sep 17 00:00:00 2001
From: Justin Wernick <justin@worthe-it.co.za>
Date: Sat, 3 Dec 2022 13:59:11 +0200
Subject: Day 3

---
 2022/src/bin/day_3.rs | 100 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 100 insertions(+)
 create mode 100644 2022/src/bin/day_3.rs

(limited to '2022/src/bin')

diff --git a/2022/src/bin/day_3.rs b/2022/src/bin/day_3.rs
new file mode 100644
index 0000000..ec2d5e2
--- /dev/null
+++ b/2022/src/bin/day_3.rs
@@ -0,0 +1,100 @@
+use nom::{
+    character::complete::{line_ending, satisfy},
+    combinator::map,
+    multi::{many1, separated_list1},
+    IResult,
+};
+use std::{collections::BTreeSet, fs, iter::Iterator};
+
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let input = fs::read_to_string("inputs/day_3.txt")?;
+    let rucksacks = Rucksacks::parser(&input).unwrap().1;
+    dbg!(rucksacks.disorder_sum());
+    dbg!(rucksacks.groups_sum());
+    Ok(())
+}
+
+#[derive(Debug, PartialEq, Eq, Clone)]
+struct Rucksacks(Vec<Rucksack>);
+
+#[derive(Debug, PartialEq, Eq, Clone)]
+struct Rucksack {
+    front: BTreeSet<ItemType>,
+    back: BTreeSet<ItemType>,
+}
+
+#[derive(Debug, PartialEq, Eq, Clone, PartialOrd, Ord)]
+struct ItemType(char);
+
+impl Rucksacks {
+    fn parser(input: &str) -> IResult<&str, Rucksacks> {
+        map(separated_list1(line_ending, Rucksack::parser), Rucksacks)(input)
+    }
+
+    fn disorder_sum(&self) -> u32 {
+        self.0.iter().map(|r| r.intersection_priority()).sum()
+    }
+
+    fn groups_sum(&self) -> u32 {
+        self.0
+            .chunks(3)
+            .map(|group| {
+                let mut overlap = group[0].union();
+                for m in group.iter().skip(1) {
+                    overlap = overlap.intersection(&m.union()).cloned().collect();
+                }
+                overlap.iter().map(|c| c.priority()).sum::<u32>()
+            })
+            .sum()
+    }
+}
+
+impl Rucksack {
+    fn parser(input: &str) -> IResult<&str, Rucksack> {
+        map(many1(ItemType::parser), Rucksack::new)(input)
+    }
+
+    fn new(contents: Vec<ItemType>) -> Rucksack {
+        let mid = contents.len() / 2;
+        let front_str = &contents[0..mid];
+        let back_str = &contents[mid..];
+
+        let mut front = BTreeSet::new();
+        for c in front_str {
+            front.insert(c.clone());
+        }
+
+        let mut back = BTreeSet::new();
+        for c in back_str {
+            back.insert(c.clone());
+        }
+
+        Rucksack { front, back }
+    }
+
+    fn intersection(&self) -> BTreeSet<ItemType> {
+        self.front.intersection(&self.back).cloned().collect()
+    }
+
+    fn union(&self) -> BTreeSet<ItemType> {
+        self.front.union(&self.back).cloned().collect()
+    }
+
+    fn intersection_priority(&self) -> u32 {
+        self.intersection().iter().map(|c| c.priority()).sum()
+    }
+}
+
+impl ItemType {
+    fn parser(input: &str) -> IResult<&str, ItemType> {
+        map(satisfy(|c| c.is_alphabetic()), ItemType)(input)
+    }
+
+    fn priority(&self) -> u32 {
+        if self.0.is_uppercase() {
+            (self.0 as u32 - 'A' as u32) + 27
+        } else {
+            (self.0 as u32 - 'a' as u32) + 1
+        }
+    }
+}
-- 
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