Day 22

src/bin/day22.rs

@@ -0,0 +1,73 @@
+use itertools::{iproduct, Itertools};
+use std::collections::{HashMap, HashSet};
+
+use anyhow::{Context, Result};
+
+const MALFORMED: &str = "malformed input";
+
+fn main() -> Result<()> {
+    let filename = std::env::args()
+        .nth(1)
+        .context("./day22 <path to puzzle input>")?;
+    let input = std::fs::read_to_string(filename)?;
+
+    let mut blocks = Vec::new();
+    for line in input.lines() {
+        let (a, b) = line.split_once(['~']).context(MALFORMED)?;
+        let mut ai = a.split(',').map(|s| s.parse::<usize>().unwrap());
+        let mut bi = b.split(',').map(|s| s.parse::<usize>().unwrap());
+        let (xa, ya, za) = ai.next_tuple().context(MALFORMED)?;
+        let (xb, yb, zb) = bi.next_tuple().context(MALFORMED)?;
+        blocks.push([(za, zb), (xa, xb), (ya, yb)]);
+    }
+
+    blocks.sort();
+
+    let mut slice = vec![vec![(0, 0); 10]; 10];
+    let mut bearing = HashSet::new();
+    let mut support = HashMap::new();
+    for ([z, x, y], id) in blocks.iter_mut().zip(1..) {
+        let z_max = iproduct!(x.0..=x.1, y.0..=y.1)
+            .map(|(x, y)| slice[x][y].1)
+            .reduce(std::cmp::max)
+            .unwrap();
+
+        let supports = iproduct!(x.0..=x.1, y.0..=y.1)
+            .filter(|(x, y)| slice[*x][*y].1 == z_max)
+            .map(|(x, y)| slice[x][y].0)
+            .collect::<HashSet<_>>();
+
+        if supports.len() == 1 {
+            bearing.insert(*supports.iter().next().unwrap());
+        }
+
+        support.insert(id, supports);
+
+        for (x, y) in iproduct!(x.0..=x.1, y.0..=y.1) {
+            slice[x][y].0 = id;
+            slice[x][y].1 = z_max + z.1 - z.0 + 1;
+        }
+    }
+
+    let part1 = blocks.len() - bearing.len() + 1;
+
+    let mut bearers = HashMap::from([(0, HashSet::new())]);
+    for id in 1..=blocks.len() {
+        let mut b = support[&id]
+            .iter()
+            .map(|id| bearers.get(id).unwrap())
+            .cloned()
+            .reduce(|a, b| &a & &b)
+            .unwrap_or_else(|| HashSet::new());
+
+        b.insert(id);
+        bearers.insert(id, b);
+    }
+
+    let part2 = bearers.values().map(|v| v.len()).sum::<usize>() - blocks.len();
+
+    println!("1) {}", part1);
+    println!("2) {}", part2);
+
+    Ok(())
+}