Refactor out common code

2022/src/common.rs

@@ -133,3 +133,42 @@ pub fn get_both<T>(slice: &mut [T], first: usize, second: usize) -> (&mut T, &mu
         Ordering::Equal => panic!("Tried to get the same index twice {first}"),
     }
 }
+
+#[derive(Default)]
+pub struct IndexSet(Vec<u32>);
+
+impl IndexSet {
+    pub fn with_capacity(capacity: usize) -> Self {
+        Self(Vec::with_capacity(
+            capacity / std::mem::size_of::<u32>() / 8,
+        ))
+    }
+
+    fn ensure_item(&mut self, item: usize) -> &mut u32 {
+        if self.0.len() <= item {
+            self.0.resize(item + 1, 0);
+        }
+
+        &mut self.0[item]
+    }
+
+    #[inline]
+    fn index(index: usize) -> (usize, u8) {
+        const PER_ENTRY: usize = 8 * std::mem::size_of::<u32>();
+
+        (index / PER_ENTRY, (index % PER_ENTRY) as u8)
+    }
+
+    pub fn insert(&mut self, index: usize) -> bool {
+        let (entry, pos) = Self::index(index);
+
+        let item = self.ensure_item(entry);
+
+        if *item & (1 << pos) != 0 {
+            false
+        } else {
+            *item |= 1 << pos;
+            true
+        }
+    }
+}

2022/src/day12.rs

@@ -3,16 +3,23 @@ use std::collections::VecDeque;
 use anyhow::Context;
 use anyhow::Result;
 
+use crate::common::IndexSet;
+
 fn can_travel(from: u8, to: u8) -> bool {
     match (from, to) {
-        (b'S', b'a'..=b'z') => true,
+        (b'S', b'a'..=b'b') => true,
         (b'y'..=b'z', b'E') => true,
         (b'a'..=b'z', b'a'..=b'z') => to <= from || to - from == 1,
         _ => false,
     }
 }
 
-pub fn part1(input: &[u8]) -> Result<String> {
+fn parts_common(
+    input: &[u8],
+    starting_symbol: u8,
+    is_end: impl Fn(u8) -> bool,
+    accessible: impl Fn(u8, u8) -> bool,
+) -> Result<String> {
     let width = input
         .iter()
         .position(|&c| c == b'\n')
@@ -21,22 +28,21 @@ pub fn part1(input: &[u8]) -> Result<String> {
 
     let starting_pos = input
         .iter()
-        .position(|&c| c == b'S')
+        .position(|&c| c == starting_symbol)
         .context("Could not find starting position")?;
 
-    let mut visited = vec![false; input.len()];
+    let mut visited = IndexSet::with_capacity(input.len());
 
     let mut todo = VecDeque::new();
     todo.push_back((0, starting_pos));
 
     while let Some((dist, pos)) = todo.pop_front() {
-        if input[pos] == b'E' {
+        if is_end(input[pos]) {
             return Ok(dist.to_string());
         }
 
         let mut add_todo = |new: usize| {
-            if can_travel(input[pos], input[new]) && !visited[new] {
-                visited[new] = true;
+            if accessible(input[pos], input[new]) && visited.insert(new) {
                 todo.push_back((dist + 1, new));
             }
         };
@@ -61,53 +67,17 @@ pub fn part1(input: &[u8]) -> Result<String> {
     anyhow::bail!("Did not find a valid route")
 }
 
+pub fn part1(input: &[u8]) -> Result<String> {
+    parts_common(input, b'S', |b| b == b'E', can_travel)
+}
+
 pub fn part2(input: &[u8]) -> Result<String> {
-    let width = input
-        .iter()
-        .position(|&c| c == b'\n')
-        .context("No newlines in input")?
-        + 1;
-
-    let starting_pos = input
-        .iter()
-        .position(|&c| c == b'E')
-        .context("Could not find starting position")?;
-
-    let mut visited = vec![false; input.len()];
-
-    let mut todo = VecDeque::new();
-    todo.push_back((0, starting_pos));
-
-    while let Some((dist, pos)) = todo.pop_front() {
-        if input[pos] == b'a' || input[pos] == b'S' {
-            return Ok(dist.to_string());
-        }
-
-        let mut add_todo = |new: usize| {
-            if can_travel(input[new], input[pos]) && !visited[new] {
-                visited[new] = true;
-                todo.push_back((dist + 1, new));
-            }
-        };
-
-        if pos % width != 0 {
-            add_todo(pos - 1);
-        }
-
-        if pos % width != width - 1 {
-            add_todo(pos + 1);
-        }
-
-        if pos >= width {
-            add_todo(pos - width);
-        }
-
-        if pos + width < input.len() {
-            add_todo(pos + width);
-        }
-    }
-
-    anyhow::bail!("Did not find a valid route")
+    parts_common(
+        input,
+        b'E',
+        |b| b == b'a' || b == b'S',
+        |a, b| can_travel(b, a),
+    )
 }
 
 #[cfg(test)]