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-rw-r--r--day08b/Cargo.toml11
-rw-r--r--day08b/examples/input.txt99
-rw-r--r--day08b/examples/test.txt5
-rw-r--r--day08b/src/main.rs120
4 files changed, 235 insertions, 0 deletions
diff --git a/day08b/Cargo.toml b/day08b/Cargo.toml
new file mode 100644
index 0000000..e71c2cd
--- /dev/null
+++ b/day08b/Cargo.toml
@@ -0,0 +1,11 @@
+[package]
+name = "day08b"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+clap = { version = "3.2.20", features = ["derive"] }
+nom = "7.1.1"
+itertools = "0.10.5"
diff --git a/day08b/examples/input.txt b/day08b/examples/input.txt
new file mode 100644
index 0000000..a82f905
--- /dev/null
+++ b/day08b/examples/input.txt
@@ -0,0 +1,99 @@
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diff --git a/day08b/examples/test.txt b/day08b/examples/test.txt
new file mode 100644
index 0000000..16d6fbd
--- /dev/null
+++ b/day08b/examples/test.txt
@@ -0,0 +1,5 @@
+30373
+25512
+65332
+33549
+35390
diff --git a/day08b/src/main.rs b/day08b/src/main.rs
new file mode 100644
index 0000000..c9d3a52
--- /dev/null
+++ b/day08b/src/main.rs
@@ -0,0 +1,120 @@
+/// --- Part Two ---
+///
+/// Content with the amount of tree cover available, the Elves just need to know the best spot to
+/// build their tree house: they would like to be able to see a lot of trees.
+///
+/// To measure the viewing distance from a given tree, look up, down, left, and right from that
+/// tree; stop if you reach an edge or at the first tree that is the same height or taller than the
+/// tree under consideration. (If a tree is right on the edge, at least one of its viewing
+/// distances will be zero.)
+///
+/// The Elves don't care about distant trees taller than those found by the rules above; the
+/// proposed tree house has large eaves to keep it dry, so they wouldn't be able to see higher than
+/// the tree house anyway.
+///
+/// In the example above, consider the middle 5 in the second row:
+///
+/// ```
+/// 30373
+/// 25512
+/// 65332
+/// 33549
+/// 35390
+/// ```
+///
+/// Looking up, its view is not blocked; it can see 1 tree (of height 3).
+/// Looking left, its view is blocked immediately; it can see only 1 tree (of height 5, right
+/// next to it).
+/// Looking right, its view is not blocked; it can see 2 trees.
+/// Looking down, its view is blocked eventually; it can see 2 trees (one of height 3, then the
+/// tree of height 5 that blocks its view).
+///
+/// A tree's scenic score is found by multiplying together its viewing distance in each of the four
+/// directions. For this tree, this is 4 (found by multiplying 1 * 1 * 2 * 2).
+///
+/// However, you can do even better: consider the tree of height 5 in the middle of the fourth row:
+///
+/// ```
+/// 30373
+/// 25512
+/// 65332
+/// 33549
+/// 35390
+/// ```
+///
+/// Looking up, its view is blocked at 2 trees (by another tree with a height of 5).
+/// Looking left, its view is not blocked; it can see 2 trees.
+/// Looking down, its view is also not blocked; it can see 1 tree.
+/// Looking right, its view is blocked at 2 trees (by a massive tree of height 9).
+///
+/// This tree's scenic score is 8 (2 * 2 * 1 * 2); this is the ideal spot for the tree house.
+///
+/// Consider each tree on your map. What is the highest scenic score possible for any tree?
+use clap::Parser;
+use itertools::Itertools;
+
+use std::fs::File;
+use std::io::prelude::*;
+use std::io::BufReader;
+use std::path::PathBuf;
+
+const FILEPATH: &'static str = "examples/input.txt";
+
+#[derive(Parser, Debug)]
+#[clap(author, version, about, long_about = None)]
+struct Cli {
+ #[clap(short, long, default_value = FILEPATH)]
+ file: PathBuf,
+}
+
+fn main() {
+ let args = Cli::parse();
+
+ let file = File::open(&args.file).unwrap();
+ let reader = BufReader::new(file);
+ let grid = reader
+ .lines()
+ .map(|l| {
+ l.unwrap()
+ .chars()
+ .map(|c| c.to_digit(10).unwrap() as u8)
+ .collect_vec()
+ })
+ .collect_vec();
+
+ let xdim = grid.len();
+ let ydim = grid[0].len();
+
+ let res = (1..(xdim - 1))
+ .cartesian_product(1..(ydim - 1))
+ .map(|(idx, idy)| {
+ let tree = grid[idx][idy];
+ let top = (0..idx)
+ .rev()
+ .map(|t| tree as i32 - grid[t][idy] as i32)
+ .position(|diff| diff <= 0)
+ .unwrap_or(idx - 1)
+ + 1;
+ let bottom = ((idx + 1)..xdim)
+ .map(|t| tree as i32 - grid[t][idy] as i32)
+ .position(|diff| diff <= 0)
+ .unwrap_or((xdim - idx) - 2)
+ + 1;
+ let left = (0..idy)
+ .rev()
+ .map(|t| tree as i32 - grid[idx][t] as i32)
+ .position(|diff| diff <= 0)
+ .unwrap_or(idy - 1)
+ + 1;
+ let right = ((idy + 1)..ydim)
+ .map(|t| tree as i32 - grid[idx][t] as i32)
+ .position(|diff| diff <= 0)
+ .unwrap_or((ydim - idy) - 2)
+ + 1;
+ top * bottom * left * right
+ })
+ .max()
+ .unwrap();
+
+ println!("{res:?}");
+}