Implement 2022 day 17 part 1

2022/src/common.rs

@@ -176,6 +176,15 @@ impl IndexSet {
             true
         }
     }
+
+    pub fn contains(&self, index: usize) -> bool {
+        let (entry, pos) = Self::index(index);
+
+        self.0
+            .get(entry)
+            .map(|&entry| (entry & (1 << pos) != 0))
+            .unwrap_or(false)
+    }
 }
 
 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]

2022/src/day17.rs

@@ -1,9 +1,124 @@
 use anyhow::Result;
 
-pub fn part1(_input: &[u8]) -> Result<String> {
-    anyhow::bail!("not implemented")
+use crate::common::IndexSet;
+
+const SHAPES: [&[&[bool]]; 5] = [
+    &[&[true; 4]],
+    &[&[false, true, false], &[true; 3], &[false, true, false]],
+    &[&[false, false, true], &[false, false, true], &[true; 3]],
+    &[&[true], &[true], &[true], &[true]],
+    &[&[true; 2], &[true; 2]],
+];
+
+const WIDTH: usize = 7;
+
+#[allow(unused)]
+fn print_cavern(cavern: &IndexSet, max_height: usize) {
+    for y in (0..=max_height).rev() {
+        for x in 0..7 {
+            print!(
+                "{}",
+                if cavern.contains(y * WIDTH + x) {
+                    '#'
+                } else {
+                    '.'
+                }
+            );
+        }
+        println!();
+    }
+}
+
+pub fn part1(input: &[u8]) -> Result<String> {
+    // Poor man's trim()
+    let input = if input[input.len() - 1] == b'\n' {
+        &input[..input.len() - 1]
+    } else {
+        input
+    };
+
+    let mut cavern = IndexSet::default();
+    let mut max_height = 0;
+
+    let mut gusts = input
+        .iter()
+        .cycle()
+        .map(|&b| if b == b'<' { -1 } else { 1 });
+
+    for &shape in SHAPES.iter().cycle().take(2022) {
+        let mut x = 2usize;
+        let mut y = max_height + shape.len() + 2;
+
+        // Acquire gust of wind
+        'falling: for offset in gusts.by_ref() {
+            if let Some(nx) = x.checked_add_signed(offset) {
+                let mut should_move = true;
+
+                'collision: for (row, line) in shape.iter().enumerate() {
+                    if nx + line.len() > WIDTH {
+                        should_move = false;
+                        break 'collision;
+                    }
+
+                    for (col, &on) in line.iter().enumerate() {
+                        if on && cavern.contains((y - row) * WIDTH + nx + col) {
+                            should_move = false;
+                            break 'collision;
+                        }
+                    }
+                }
+
+                if should_move {
+                    x = nx;
+                }
+            } else {
+                // Hit the left wall
+            }
+
+            // Move down if possible
+            if y >= shape.len() {
+                let ny = y - 1;
+                for (row, line) in shape.iter().enumerate() {
+                    // No width check, should not hit that on the way down.
+                    for (col, &on) in line.iter().enumerate() {
+                        if on && cavern.contains((ny - row) * WIDTH + x + col) {
+                            break 'falling;
+                        }
+                    }
+                }
+                y = ny;
+            } else {
+                break 'falling;
+            }
+        }
+
+        // If we get here we've successfully stopped falling
+        max_height = max_height.max(y + 1);
+
+        for (row, line) in shape.iter().enumerate() {
+            for (col, &on) in line.iter().enumerate() {
+                if on {
+                    cavern.insert((y - row) * WIDTH + x + col);
+                }
+            }
+        }
+    }
+
+    Ok(max_height.to_string())
 }
 
 pub fn part2(_input: &[u8]) -> Result<String> {
     anyhow::bail!("not implemented")
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const SAMPLE: &[u8] = include_bytes!("samples/17.txt");
+
+    #[test]
+    fn sample_part1() {
+        assert_eq!(part1(SAMPLE).unwrap(), "3068");
+    }
+}

2022/src/samples/17.txt

@@ -0,0 +1 @@
+>>><<><>><<<>><>>><<<>>><<<><<<>><>><<>>