day03: Add part 1 solution

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;
+
+	for line in reader.lines() {
+		let line = line?;
+		let (c1, c2) = line.split_at(line.len() / 2);
+		let c1_set = set_from_str(c1);
+		let c2_set = set_from_str(c2);
+		sum += c1_set.intersection(&c2_set).sum::<u32>();
+	}
+
+	println!("{}", sum);
+
+    Ok(())
+}