Implement 2022 day 8 part 1

2022/src/day08.rs

@@ -1,9 +1,81 @@
+use anyhow::Context;
 use anyhow::Result;
 
-pub fn part1(_input: &[u8]) -> Result<String> {
-    todo!()
+#[inline]
+fn stripe<'a>(
+    values: impl IntoIterator<Item = &'a u8>,
+    visible: impl IntoIterator<Item = &'a mut bool>,
+) {
+    let mut max = 0;
+
+    for (&val, visible) in values.into_iter().zip(visible) {
+        if val > max {
+            max = val;
+            *visible = true;
+
+            if val == b'9' {
+                return;
+            }
+        }
+    }
+}
+
+pub fn part1(input: &[u8]) -> Result<String> {
+    let width = input
+        .iter()
+        .position(|&b| b == b'\n')
+        .context("Single row field")?;
+    let height = input.len() / (width + 1); // Include newlines
+
+    let mut visible = vec![false; width * height];
+
+    // Horizontal striping
+    for (y, row) in input.chunks_exact(width + 1).enumerate() {
+        // First, left to right
+        stripe(&row[..width], &mut visible[(y * width)..]);
+
+        // Then right to left
+        stripe(
+            row[..width].iter().rev(),
+            visible[(y * width)..(y * width + width)].iter_mut().rev(),
+        );
+    }
+
+    // Vertical striping
+    for x in 0..width {
+        // Top to bottom
+        stripe(
+            input[x..].iter().step_by(width + 1),
+            visible[x..].iter_mut().step_by(width),
+        );
+
+        // Bottom to top
+        stripe(
+            input[x..].iter().step_by(width + 1).rev(),
+            visible[x..].iter_mut().step_by(width).rev(),
+        )
+    }
+
+    Ok(visible.into_iter().filter(|&b| b).count().to_string())
 }
 
 pub fn part2(_input: &[u8]) -> Result<String> {
     todo!()
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const SAMPLE: &[u8] = include_bytes!("samples/08.txt");
+
+    #[test]
+    fn sample_part1() {
+        assert_eq!(part1(SAMPLE).unwrap(), "21");
+    }
+
+    #[test]
+    fn sample_part2() {
+        assert_eq!(part2(SAMPLE).unwrap(), "8");
+    }
+}

2022/src/samples/08.txt

@@ -0,0 +1,5 @@
+30373
+25512
+65332
+33549
+35390