From de5ab93a8b6613438f6c5ae5a277ae21c0bf4a5e Mon Sep 17 00:00:00 2001
From: Tyler Beckman <ty@myriation.xyz>
Date: Wed, 11 Dec 2024 23:10:27 -0700
Subject: [PATCH] Day 12 p1

---
 Cargo.toml     |  4 +++
 day12/part1.rs | 88 ++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 92 insertions(+)
 create mode 100644 day12/part1.rs

diff --git a/Cargo.toml b/Cargo.toml
index 57c7c47..67f5862 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -6,3 +6,7 @@ edition = "2021"
 [[bin]]
 name = "d11p2"
 path = "day11/part2.rs"
+
+[[bin]]
+name = "d12p1"
+path = "day12/part1.rs"
diff --git a/day12/part1.rs b/day12/part1.rs
new file mode 100644
index 0000000..d6999e3
--- /dev/null
+++ b/day12/part1.rs
@@ -0,0 +1,88 @@
+#![feature(let_chains)]
+use std::collections::{HashSet, VecDeque};
+
+const GRID_SIZE: usize = 140;
+
+fn dfs(grid: &[[char; GRID_SIZE]; GRID_SIZE], start: (usize, usize)) -> HashSet<(usize, usize)> {
+    let mut queue = VecDeque::from([start]);
+    let mut set = HashSet::from([start]);
+    let plant_type = grid[start.0][start.1];
+
+    while let Some(next) = queue.pop_front() {
+        let to_check = [
+            (next.0 + 1, next.1),
+            (next.0.wrapping_sub(1), next.1),
+            (next.0, next.1 + 1),
+            (next.0, next.1.wrapping_sub(1)),
+        ];
+        for pos in to_check {
+            if set.contains(&pos) {
+                continue;
+            }
+
+            if let Some(plant) = grid.get(pos.0).and_then(|r| r.get(pos.1))
+                && *plant == plant_type
+            {
+                queue.push_back(pos);
+                set.insert(pos);
+            }
+        }
+    }
+
+    set
+}
+
+fn main() {
+    let mut input_iter = include_str!("input.txt").lines().map(|l| {
+        let mut iter = l.chars();
+        std::array::from_fn::<_, GRID_SIZE, _>(|_| iter.next().unwrap())
+    });
+    let grid: [_; GRID_SIZE] = std::array::from_fn(|_| input_iter.next().unwrap());
+
+    // Parse all independent regions
+    let mut regions = Vec::<HashSet<(usize, usize)>>::new();
+    for row in 0..GRID_SIZE {
+        for col in 0..GRID_SIZE {
+            if regions.iter().all(|region| !region.contains(&(row, col))) {
+                regions.push(dfs(&grid, (row, col)));
+            }
+        }
+    }
+
+    // Sanity check -> are there any duplicated nodes between the regions?
+    assert_eq!(
+        regions.iter().map(|r| r.len()).sum::<usize>(),
+        regions
+            .iter()
+            .flatten()
+            .collect::<HashSet<&(usize, usize)>>()
+            .len()
+    );
+
+    // Calculate area and perimeter of each
+    let mut sum = 0;
+    for region in regions.into_iter() {
+        let area = region.len();
+        let mut perimeter_set = Vec::<(Option<usize>, Option<usize>)>::new();
+        for pos in region.iter() {
+            // None in a position is a special case meaning "overfilled in the negative direction"
+            // Since we don't actually access the point there, it just gets treated like -1 would
+            let to_check = [
+                (pos.0.checked_add(1), Some(pos.1)),
+                (pos.0.checked_sub(1), Some(pos.1)),
+                (Some(pos.0), pos.1.checked_add(1)),
+                (Some(pos.0), pos.1.checked_sub(1)),
+            ];
+            for outer_pos in to_check {
+                if (outer_pos.0.is_none() || outer_pos.1.is_none())
+                    || !region.contains(&(outer_pos.0.unwrap(), outer_pos.1.unwrap()))
+                {
+                    perimeter_set.push(outer_pos);
+                }
+            }
+        }
+        sum += area * perimeter_set.len();
+    }
+
+    println!("Result: {sum}");
+}