2018 day 2

Author: ictrobot

crates/utils/src/array.rs

@@ -159,6 +159,25 @@ impl<T, const N: usize> ArrayVec<T, N> {
     pub fn is_full(&self) -> bool {
         self.len == N
     }
+
+    /// Returns the backing array.
+    ///
+    /// Any items after the current length will be set to the default value.
+    ///
+    /// # Examples
+    /// ```
+    /// # use utils::array::ArrayVec;
+    /// let mut vec: ArrayVec<i32, 5> = ArrayVec::new();
+    /// vec.push(1).unwrap();
+    /// vec.push(2).unwrap();
+    /// vec.push(3).unwrap();
+    /// vec.pop().unwrap();
+    /// assert_eq!(vec.into_array(), [1, 2, 0, 0, 0]);
+    /// ```
+    #[inline]
+    pub fn into_array(self) -> [T; N] {
+        self.data
+    }
 }
 
 impl<T, const N: usize> Deref for ArrayVec<T, N> {

crates/year2018/src/day02.rs

@@ -0,0 +1,55 @@
+use std::collections::HashSet;
+use utils::array::ArrayVec;
+use utils::prelude::*;
+
+/// Finding near-match IDs.
+#[derive(Clone, Debug)]
+pub struct Day02 {
+    ids: Vec<ArrayVec<u8, 32>>,
+}
+
+impl Day02 {
+    pub fn new(input: &str, _: InputType) -> Result<Self, InputError> {
+        Ok(Self {
+            ids: parser::byte_range(b'a'..=b'z')
+                .repeat_arrayvec(parser::noop(), 1)
+                .parse_lines(input)?,
+        })
+    }
+
+    #[must_use]
+    #[expect(clippy::manual_contains, reason = ".iter().any() is faster here")]
+    pub fn part1(&self) -> u32 {
+        let mut twos = 0;
+        let mut threes = 0;
+        for id in &self.ids {
+            let mut freq = [0u8; 26];
+            for &i in id {
+                freq[(i - b'a') as usize] += 1;
+            }
+            twos += u32::from(freq.iter().any(|&x| x == 2));
+            threes += u32::from(freq.iter().any(|&x| x == 3));
+        }
+        twos * threes
+    }
+
+    #[must_use]
+    pub fn part2(&self) -> String {
+        let mut seen = HashSet::with_capacity(self.ids.len());
+        for column in 0..self.ids[0].capacity() {
+            for mut id in self.ids.iter().map(|id| id.clone().into_array()) {
+                id[column] = 0;
+                if !seen.insert(id) {
+                    return id.iter().filter(|&&x| x != 0).map(|&x| x as char).collect();
+                }
+            }
+            seen.clear();
+        }
+        panic!("no solution found")
+    }
+}
+
+examples!(Day02 -> (u32, &'static str) [
+    {input: "abcdef\nbababc\nabbcde\nabcccd\naabcdd\nabcdee\nababab", part1: 12},
+    {input: "abcde\nfghij\nklmno\npqrst\nfguij\naxcye\nwvxyz", part2: "fgij"},
+]);

crates/year2018/src/lib.rs

@@ -3,4 +3,5 @@
 
 utils::year!(2018 => year2018, ${
     1 => day01::Day01,
+    2 => day02::Day02,
 });