Solution for 2022/day03-part2

2022/day03-part2/Cargo.toml

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+[package]
+name = "day03-part2"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

2022/day03-part2/src/main.rs

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+use std::collections::HashSet;
+
+fn main() {
+    // Use command line arguments to specify the input filename.
+    let args: Vec<String> = std::env::args().collect();
+    if args.len() < 2 {
+        panic!("Usage: ./main <input-file>\nNo input file provided. Exiting.");
+    }
+
+    // Next, read the contents of the input file into a string for easier processing.
+    let input = std::fs::read_to_string(&args[1]).expect("Error opening file");
+    // Line-by-line processing is easiest.
+    let mut input = input.lines();
+
+    // --- TASK BEGIN ---
+    let mut total = 0;
+    while let Some(line) = input.next() {
+        // Read the next three lines and turn them into HashSets.
+        let first: HashSet<char> = line.chars().collect();
+        let second: HashSet<char> = input.next().unwrap().chars().collect();
+        let third: HashSet<char> = input.next().unwrap().chars().collect();
+        // Use set intersection to determine the item that's common to all three sets.
+        let item = *first.intersection(&second).copied().collect::<HashSet<char>>().intersection(&third).next().unwrap();
+        // Calculate the priority.
+        let priority = match item {
+            item if item.is_ascii_lowercase() => (item as u32) - ('a' as u32) + 1,
+            item if item.is_ascii_uppercase() => (item as u32) - ('A' as u32) + 27,
+            _ => {panic!("Character out of range")}
+        };
+        // Accumulate the priorities.
+        total += priority;
+    }
+    println!("Total priority: {total}");
+}
+