day 3

.gitignore

@@ -1 +1,2 @@
 input.txt
+/*/target

d1/.gitignore

@@ -1 +0,0 @@
-/target

d2/.gitignore

@@ -1 +0,0 @@
-/target

d3/Cargo.lock

@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "d3"
+version = "0.1.0"

d3/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "d3"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

d3/src/main.rs

@@ -0,0 +1,44 @@
+use std::{io::Result, fs::read_to_string, collections::HashSet};
+
+pub fn priority(x: u8) -> u32 {
+    (match x {
+        0x61..=0x7a => x - 0x61 + 1,
+        0x41..=0x5a => x - 0x41 + 27,
+        _ => unreachable!()
+    }) as u32
+}
+
+fn main() -> Result<()> {
+    let mut p1_priority: u32 = 0;
+    let mut p2_priority: u32 = 0;
+
+    let mut i = 0;
+    let mut elves: Vec<HashSet<_>> = Vec::new();
+
+    for line in read_to_string("input.txt")?.split("\n") {
+        if line.is_empty() { continue; }
+        let bytes = line.as_bytes();
+
+        let (first_half, second_half) = bytes.split_at(bytes.len() / 2);
+        let in_first_half = first_half.iter().copied().collect::<HashSet<_>>();
+        let in_second_half = second_half.iter().copied().collect::<HashSet<_>>();
+        let in_both_halves = in_first_half.intersection(&in_second_half).copied().next().unwrap();
+        p1_priority += priority(in_both_halves);
+
+        let items = bytes.iter().copied().collect::<HashSet<_>>();
+        elves.push(items.clone());
+        if i == 2 {
+            let badge = items.iter().filter(|item| elves.iter().filter(|elf| elf.contains(item)).count() == 3).copied().next().unwrap();
+            p2_priority += priority(badge);
+            elves.clear();
+            i = 0;
+        } else {
+            i += 1;
+        }
+    }
+
+    println!("part 1: {}", p1_priority);
+    println!("part 2: {}", p2_priority);
+
+    Ok(())
+}