day 3

day03/src/main.rs

@@ -0,0 +1,52 @@
+use rustc_hash::FxHashSet;
+use std::io::{self, BufRead};
+
+const LOWERCASE_ASCII_OFFSET: usize = 64;
+const UPPERCASE_ASCII_OFFSET: usize = 32;
+const LOWERCASE_ALPHA_OFFSET: usize = 26;
+
+fn main() {
+    let lines = io::stdin().lock().lines().map(|l| l.unwrap());
+    let mut first_half: FxHashSet<char>;
+    let mut second_half: FxHashSet<char>;
+    let mut p1_sum = 0usize;
+    let mut p2_sum = 0usize;
+
+    let mut group_set: FxHashSet<char>;
+    let mut groups: Vec<String> = Vec::new();
+
+    for line in lines {
+        groups.push(line.clone());
+        if groups.len() == 3 {
+            group_set = groups[0]
+                .chars()
+                .collect::<FxHashSet<char>>()
+                .intersection(&groups[1].chars().collect())
+                .copied()
+                .collect::<FxHashSet<char>>()
+                .intersection(&groups[2].chars().collect())
+                .copied()
+                .collect();
+            p2_sum += type_to_priority(group_set.iter().next().unwrap());
+            groups.clear();
+        }
+
+        let (first, second) = line.split_at(line.len() / 2);
+        first_half = first.chars().collect();
+        second_half = second.chars().collect();
+        let shared_type = first_half.intersection(&second_half).next().unwrap();
+        p1_sum += type_to_priority(shared_type);
+    }
+    println!("P1: {}, P2: {}", p1_sum, p2_sum);
+}
+
+fn type_to_priority(ptype: &char) -> usize {
+    let mut ascii_val = *ptype as usize;
+    ascii_val -= LOWERCASE_ASCII_OFFSET;
+    if ascii_val > UPPERCASE_ASCII_OFFSET {
+        ascii_val -= UPPERCASE_ASCII_OFFSET
+    } else {
+        ascii_val += LOWERCASE_ALPHA_OFFSET
+    }
+    ascii_val
+}