Day 3, Part 2

2022/aoc2022/src/day3.rs

@@ -1,27 +1,52 @@
 use std::collections::HashSet;
-use std::collections::hash_set::{Intersection, IntoIter};
 use std::io::Result;
-use std::iter::Sum;
+use std::iter::Iterator;
 
 use crate::file::line_reader_for_file;
 
+fn priority_items_in_knapsack(knapsack: &str) -> Vec<char> {
+    assert!(knapsack.len() % 2 == 0);
+
+    let compartment_size: usize = knapsack.len() / 2;
+
+    let (left_compartment, right_compartment) = knapsack.split_at(compartment_size);
+    let left_compartment_set: HashSet<char> = HashSet::from_iter(left_compartment.chars());
+    let right_compartment_set: HashSet<char> = HashSet::from_iter(right_compartment.chars());
+
+    left_compartment_set.intersection(&right_compartment_set).map(|c| *c).collect()
+}
+
+fn badge_for_group(group: (&str, &str, &str)) -> Vec<char> {
+    let a_set: HashSet<char> = HashSet::from_iter(group.0.chars());
+    let b_set: HashSet<char> = HashSet::from_iter(group.1.chars());
+    let c_set: HashSet<char> = HashSet::from_iter(group.2.chars());
+
+    let ab_intersection: HashSet<char> = a_set
+        .intersection(&b_set)
+        .map(|c| *c)
+        .collect();
+    ab_intersection
+        .intersection(&c_set)
+        .map(|c| *c)
+        .collect()
+}
+
 pub fn main(filename: &str) -> Result<()> {
-    let line_reader = line_reader_for_file(filename)?;
+    let mut line_reader = line_reader_for_file(filename)?.peekable();
 
     let mut priority_letters: Vec<char> = Vec::new();
+    let mut badges: Vec<char> = Vec::new();
 
-    for line in line_reader {
-        let line = line?;
-        assert!(line.len() % 2 == 0);
+    while line_reader.peek().is_some() {
+        let a = line_reader.next().unwrap()?;
+        let b = line_reader.next().unwrap()?;
+        let c = line_reader.next().unwrap()?;
 
-        let compartment_size: usize = line.len() / 2;
+        priority_letters.extend(priority_items_in_knapsack(&a));
+        priority_letters.extend(priority_items_in_knapsack(&b));
+        priority_letters.extend(priority_items_in_knapsack(&c));
 
-        let (left_compartment, right_compartment) = line.split_at(compartment_size);
-        let left_compartment_set: HashSet<char> = HashSet::from_iter(left_compartment.chars());
-        let right_compartment_set: HashSet<char> = HashSet::from_iter(right_compartment.chars());
-
-        let intersection = left_compartment_set.intersection(&right_compartment_set);
-        priority_letters.extend(intersection);
+        badges.extend(badge_for_group((&a, &b, &c)));
     }
 
     const LOWERCASE_A_SCORE: u32 = 'a' as u32;
@@ -42,5 +67,20 @@ pub fn main(filename: &str) -> Result<()> {
 
     println!("Part 1: sum of scores of all priority items: {}", sum_of_scored_priority_letters);
 
+    let sum_of_badges: u32 =
+        badges
+            .iter()
+            .map(|c| -> u32 {
+                let char_value: u32 = (*c).into();
+                if c.is_lowercase() {
+                    char_value - LOWERCASE_A_SCORE + 1
+                } else {
+                    char_value - UPPERCASE_A_SCORE + 27
+                }
+            })
+            .sum();
+
+    println!("Part 2: sum of badges: {}", sum_of_badges);
+
     Ok(())
 }