complete day 3

1 files changed, 94 insertions, 0 deletions

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+/// --- Part Two ---
+///
+/// As you finish identifying the misplaced items, the Elves come to you with another issue.
+///
+/// For safety, the Elves are divided into groups of three.  Every Elf carries a badge that
+/// identifies their group.  For efficiency, within each group of three Elves, the badge is the
+/// only item type carried by all three Elves.  That is, if a group's badge is item type B, then
+/// all three Elves will have item type B somewhere in their rucksack, and at most two of the Elves
+/// will be carrying any other item type.
+///
+/// The problem is that someone forgot to put this year's updated authenticity sticker on the
+/// badges.  All of the badges need to be pulled out of the rucksacks so the new authenticity
+/// stickers can be attached.
+///
+/// Additionally, nobody wrote down which item type corresponds to each group's badges.  The only
+/// way to tell which item type is the right one is by finding the one item type that is common
+/// between all three Elves in each group.
+///
+/// Every set of three lines in your list corresponds to a single group, but each group can have a
+/// different badge item type.  So, in the above example, the first group's rucksacks are the first
+/// three lines:
+///
+/// ```
+/// vJrwpWtwJgWrhcsFMMfFFhFp
+/// jqHRNqRjqzjGDLGLrsFMfFZSrLrFZsSL
+/// PmmdzqPrVvPwwTWBwg
+/// ```
+///
+/// And the second group's rucksacks are the next three lines:
+///
+/// ```
+/// wMqvLMZHhHMvwLHjbvcjnnSBnvTQFn
+/// ttgJtRGJQctTZtZT
+/// CrZsJsPPZsGzwwsLwLmpwMDw
+/// ```
+///
+/// In the first group, the only item type that appears in all three rucksacks is lowercase r; this
+/// must be their badges.  In the second group, their badge item type must be Z.
+///
+/// Priorities for these items must still be found to organize the sticker attachment efforts:
+/// here, they are 18 (r) for the first group and 52 (Z) for the second group.  The sum of these is
+/// 70.
+///
+/// Find the item type that corresponds to the badges of each three-Elf group.  What is the sum of
+/// the priorities of those item types?
+use clap::Parser;
+use itertools::Itertools;
+
+use std::fs::File;
+use std::io::prelude::*;
+use std::io::BufReader;
+use std::path::PathBuf;
+
+const FILEPATH: &'static str = "examples/input.txt";
+
+#[derive(Parser, Debug)]
+#[clap(author, version, about, long_about = None)]
+struct Cli {
+    #[clap(short, long, default_value = FILEPATH)]
+    file: PathBuf,
+}
+
+fn main() {
+    let args = Cli::parse();
+
+    let file = File::open(&args.file).unwrap();
+    let reader = BufReader::new(file);
+    let res = reader
+        .lines()
+        .map(|l| l.unwrap())
+        .chunks(3)
+        .into_iter()
+        .map(|iter| {
+            let (top, middle, bottom) = iter.collect_tuple::<(String, String, String)>().unwrap();
+            top.chars()
+                .filter(|t| middle.contains(*t) && bottom.contains(*t))
+                .map(|l| {
+                    let b = l as u8;
+                    if b > b'a' {
+                        (b - b'a') as u16 + 1
+                    } else {
+                        (b - b'A') as u16 + 27
+                    }
+                })
+                .next()
+                .unwrap()
+        })
+        .sum::<u16>();
+
+    println!(
+        "The sum of the priorities of the item that appear in both compartments of each rucksack is {}",
+        res
+    );
+}