day03: Make it solve part 2 instead

day03/Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "day03"
+version = "0.1.0"

day03/Cargo.toml

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+[package]
+name = "day03"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

day03/src/main.rs

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+use std::collections::HashSet;
+use std::error;
+use std::fs::File;
+use std::io::BufRead;
+use std::io::BufReader;
+
+
+fn set_from_str(chars: &str) -> HashSet<u32> {
+	HashSet::from_iter(chars.chars().map(|c| if c.is_uppercase() { c as u32 - 38 } else { c as u32 - 96 }))
+}
+
+
+fn main() -> Result<(), Box<dyn error::Error>> {
+	let f = File::open("input.txt")?;
+	let reader = BufReader::new(f);
+
+	let mut sum: u32 = 0;
+	let mut group_items: HashSet<u32> = HashSet::new();
+
+	for (i, line) in reader.lines().enumerate() {
+		let line = line?;
+		if group_items.is_empty() {
+			group_items = set_from_str(line.as_str());
+		} else {
+			group_items = set_from_str(line.as_str()).intersection(&group_items).cloned().collect();
+		}
+		if (i + 1) % 3 == 0 {
+			sum += group_items.iter().next().unwrap();
+			group_items.drain();
+		}
+	}
+
+	println!("{}", sum);
+
+    Ok(())
+}