From 7982e1c56fa1f7663a227c62604f9b1a151713f6 Mon Sep 17 00:00:00 2001
From: Malte Tammena <malte.tammena@pm.me>
Date: Sat, 3 Dec 2022 22:03:18 +0100
Subject: [PATCH] Some changes

---
 day03-gen-problem/src/main.rs |  7 ++--
 day03/src/bitmask.rs          | 62 +++++++++++++++++++++++++++++++++++
 day03/src/main.rs             | 48 +++++++++++++--------------
 3 files changed, 87 insertions(+), 30 deletions(-)
 create mode 100644 day03/src/bitmask.rs

diff --git a/day03-gen-problem/src/main.rs b/day03-gen-problem/src/main.rs
index 5090748..4f96410 100644
--- a/day03-gen-problem/src/main.rs
+++ b/day03-gen-problem/src/main.rs
@@ -50,12 +50,11 @@ fn replace_rand<I>(rng: &mut rand::rngs::SmallRng, list: &mut Vec<I>, item: I) {
 }
 
 fn gen_triple(rng: &mut rand::rngs::SmallRng) -> [String; 3] {
-    let amounts = ARGS.half_line_range().choose_multiple(rng, 3);
     // The badge that is shared in this triple
     let badge: char = *CHARS.choose(rng).unwrap();
-    let mut lines: Vec<String> = amounts
-        .iter()
-        .map(|&amount| {
+    let mut lines: Vec<String> = (0..3)
+        .map(|_| {
+            let amount = rng.gen_range(ARGS.half_line_range());
             debug_assert!(amount > 0);
             // The item that is shared between the halves
             let wrong_between_halves: char = *CHARS
diff --git a/day03/src/bitmask.rs b/day03/src/bitmask.rs
new file mode 100644
index 0000000..31028fd
--- /dev/null
+++ b/day03/src/bitmask.rs
@@ -0,0 +1,62 @@
+use std::ops::{BitAnd, BitOr};
+
+#[derive(Debug, Default, Clone, Copy, PartialEq, Eq)]
+pub struct Bitmask(u64);
+
+impl Bitmask {
+    #[cfg(test)]
+    pub const fn from_raw(raw: u64) -> Self {
+        Self(raw)
+    }
+    pub const fn from_alpha(alpha: &u8) -> Self {
+        // 'a' is the LSB, 'Z' is MSB
+        if *alpha <= b'Z' {
+            Self(1 << (alpha - b'A' + 26))
+        } else {
+            Self(1 << (alpha - b'a'))
+        }
+    }
+    /// Get the priority from a rucksack entry
+    pub const fn to_priority(self) -> super::Prio {
+        self.0.trailing_zeros() as usize + 1
+    }
+}
+
+impl const BitOr for Bitmask {
+    type Output = Self;
+
+    fn bitor(self, rhs: Self) -> Self::Output {
+        Self(self.0 | rhs.0)
+    }
+}
+
+impl const BitAnd for Bitmask {
+    type Output = Self;
+
+    fn bitand(self, rhs: Self) -> Self::Output {
+        Self(self.0 & rhs.0)
+    }
+}
+
+impl std::fmt::Binary for Bitmask {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{:b}", self.0)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn bitmask_works() {
+        assert_eq!(
+            crate::parse_chars::<String>("abc".into()),
+            Bitmask::from_raw(7)
+        );
+        assert_eq!(
+            crate::parse_chars::<String>("Z".into()),
+            Bitmask::from_raw(1 << 51)
+        );
+    }
+}
diff --git a/day03/src/main.rs b/day03/src/main.rs
index 63b3763..1d8c7b5 100644
--- a/day03/src/main.rs
+++ b/day03/src/main.rs
@@ -1,13 +1,18 @@
 #![allow(incomplete_features)]
 #![feature(iter_array_chunks)]
 #![feature(generic_const_exprs)]
+#![feature(const_trait_impl)]
+#![feature(const_ops)]
+use bitmask::Bitmask;
+
 use std::{
     fs::File,
     io::{BufRead, BufReader},
 };
 
+mod bitmask;
+
 type Prio = usize;
-type AsciiChar = u8;
 
 #[derive(Debug, Default)]
 enum SolvePuzzle {
@@ -23,39 +28,29 @@ trait IsTrue {}
 /// A correct assertion, of course, is true!
 impl IsTrue for Assert<true> {}
 
-/// Get the priority from a rucksack entry
-fn to_priority(char: AsciiChar) -> Prio {
-    match char {
-        // a..z have priority 1..=26
-        b'a'..=b'z' => (char - b'a' + 1) as usize,
-        // A..Z have priority 27..=52
-        b'A'..=b'Z' => (char - b'A' + 27) as usize,
-        _ => unreachable!(),
-    }
-}
-
 /// Convert the line into a list of ascii chars
-fn parse_chars(line: String) -> Vec<AsciiChar> {
-    line.as_bytes().to_vec()
+fn parse_chars<S: AsRef<str>>(line: S) -> Bitmask {
+    line.as_ref()
+        .as_bytes()
+        .iter()
+        .map(Bitmask::from_alpha)
+        .reduce(std::ops::BitOr::bitor)
+        .unwrap()
 }
 
 /// Given an array of size `N` containing lists of chars.
 /// Find the char that is contained in all `N` lists, if any.
-fn find_n_entry<const N: usize>(lists: [Vec<AsciiChar>; N]) -> Option<AsciiChar>
+fn find_n_entry<const N: usize>(lists: [Bitmask; N]) -> Option<Bitmask>
 where
     Assert<{ N > 1 }>: IsTrue,
 {
-    let mut found = lists[0].clone();
-    for list in &lists[1..] {
-        found.retain(|char| list.contains(char))
-    }
-    found.first().copied()
+    lists.into_iter().reduce(|left, right| left & right)
 }
 
-/// Split the given [`Vec`] in the middle
-fn split_line(line: Vec<AsciiChar>) -> [Vec<AsciiChar>; 2] {
+/// Split the given [`String`] in the middle
+fn split_line(line: String) -> [String; 2] {
     let (left, right) = line.split_at(line.len() / 2);
-    [left.to_vec(), right.to_vec()]
+    [left.to_string(), right.to_string()]
 }
 
 /// Solve the first puzzle:
@@ -65,11 +60,12 @@ fn solve_first_puzzle<B: BufRead>(reader: B) -> usize {
     reader
         .lines()
         .map(Result::unwrap)
+        .flat_map(split_line)
         .map(parse_chars)
-        .map(split_line)
+        .array_chunks::<2>()
         .map(find_n_entry)
         .map(Option::unwrap)
-        .map(to_priority)
+        .map(Bitmask::to_priority)
         .sum()
 }
 
@@ -84,7 +80,7 @@ fn solve_second_puzzle<B: BufRead>(reader: B) -> usize {
         .array_chunks::<3>()
         .map(find_n_entry)
         .map(Option::unwrap)
-        .map(to_priority)
+        .map(Bitmask::to_priority)
         .sum()
 }