From bccf31bf85121c2bee7f02bab167d7a71f5d75c8 Mon Sep 17 00:00:00 2001
From: Jeremy Kaplan <jdkaplan@metagram.net>
Date: Wed, 7 Dec 2022 23:05:10 -0800
Subject: [PATCH] 2022 Day 8

---
 2022/src/bin/day08.rs | 162 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 162 insertions(+)
 create mode 100644 2022/src/bin/day08.rs

diff --git a/2022/src/bin/day08.rs b/2022/src/bin/day08.rs
new file mode 100644
index 0000000..8da9fff
--- /dev/null
+++ b/2022/src/bin/day08.rs
@@ -0,0 +1,162 @@
+use std::collections::{HashMap, HashSet};
+
+const INPUT: &str = include_str!("../../input/day08.txt");
+
+fn main() {
+    let grid = Grid::new(INPUT);
+
+    let visibility = grid.count_visible();
+    let part1 = visibility.iter().filter(|(_, v)| !v.is_empty()).count();
+    println!("Part 1: {}", part1);
+
+    let scenicality = grid.score_views();
+    let part2 = *scenicality.values().max().unwrap();
+    println!("Part 2: {}", part2);
+}
+
+type RC = (usize, usize);
+
+struct Grid {
+    map: HashMap<RC, u8>,
+    rows: usize,
+    cols: usize,
+}
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
+enum Visibility {
+    Top,
+    Bottom,
+    Left,
+    Right,
+}
+
+impl Visibility {
+    fn all() -> HashSet<Self> {
+        use Visibility::*;
+        HashSet::from([Top, Bottom, Left, Right])
+    }
+}
+
+impl Grid {
+    fn new(text: &str) -> Self {
+        let mut map = HashMap::new();
+        let lines = aoc::split_lines(text);
+
+        let rows = lines.len();
+        let cols = lines[0].len();
+
+        for (row, line) in lines.iter().enumerate() {
+            for (col, num) in line.chars().enumerate() {
+                let height: u8 = num.to_string().parse().unwrap();
+                map.insert((row, col), height);
+            }
+        }
+        Self { map, rows, cols }
+    }
+
+    fn count_visible(&self) -> HashMap<RC, HashSet<Visibility>> {
+        // Assume all trees are visible from all sides until we learn that they're blocked.
+        let mut visibility: HashMap<RC, HashSet<Visibility>> = HashMap::new();
+
+        for r in 0..self.rows {
+            for c in 0..self.cols {
+                visibility.insert((r, c), Visibility::all());
+            }
+        }
+
+        for (r1, c1) in itertools::iproduct!(0..self.rows, 0..self.cols) {
+            let big = (r1, c1);
+            let h1 = self.map[&big];
+
+            for (r2, c2) in (0..r1).map(|r| (r, c1)) {
+                let lil = (r2, c2);
+                let h2 = self.map[&lil];
+
+                if h1 >= h2 {
+                    visibility.entry(lil).and_modify(|v| {
+                        v.remove(&Visibility::Bottom);
+                    });
+                }
+            }
+
+            for (r2, c2) in ((r1 + 1)..self.rows).map(|r| (r, c1)) {
+                let lil = (r2, c2);
+                let h2 = self.map[&lil];
+
+                if h1 >= h2 {
+                    visibility.entry(lil).and_modify(|v| {
+                        v.remove(&Visibility::Top);
+                    });
+                }
+            }
+
+            for (r2, c2) in (0..c1).map(|c| (r1, c)) {
+                let lil = (r2, c2);
+                let h2 = self.map[&lil];
+
+                if h1 >= h2 {
+                    visibility.entry(lil).and_modify(|v| {
+                        v.remove(&Visibility::Right);
+                    });
+                }
+            }
+
+            for (r2, c2) in ((c1 + 1)..self.cols).map(|c| (r1, c)) {
+                let lil = (r2, c2);
+                let h2 = self.map[&lil];
+
+                if h1 >= h2 {
+                    visibility.entry(lil).and_modify(|v| {
+                        v.remove(&Visibility::Left);
+                    });
+                }
+            }
+        }
+
+        visibility
+    }
+
+    fn score_views(&self) -> HashMap<RC, u64> {
+        let mut scene: HashMap<RC, u64> = HashMap::new();
+
+        for (r1, c1) in itertools::iproduct!(0..self.rows, 0..self.cols) {
+            let big = (r1, c1);
+            let h1 = self.map[&big];
+
+            let mut score = 1;
+
+            let up = (0..r1).rev().map(|r| (r, c1));
+            score *= take_until(up, |rc| self.map[rc] >= h1).len();
+
+            let down = ((r1 + 1)..self.rows).map(|r| (r, c1));
+            score *= take_until(down, |rc| self.map[rc] >= h1).len();
+
+            let left = (0..c1).rev().map(|c| (r1, c));
+            score *= take_until(left, |rc| self.map[rc] >= h1).len();
+
+            let right = ((c1 + 1)..self.cols).map(|c| (r1, c));
+            score *= take_until(right, |rc| self.map[rc] >= h1).len();
+
+            scene.insert(big, score as u64);
+        }
+
+        scene
+    }
+}
+
+// This iterator is eager because _I'm_ lazy.
+fn take_until<P>(mut iter: impl Iterator<Item = RC>, mut predicate: P) -> Vec<RC>
+where
+    P: FnMut(&RC) -> bool,
+{
+    let mut v = vec![];
+    loop {
+        let Some(i) = iter.next() else { break };
+        v.push(i);
+
+        if predicate(&i) {
+            break;
+        }
+    }
+    v
+}