day21: done

Author: tung

Cargo.lock

@@ -40,6 +40,7 @@ members = [
     "day19pt2",
     "day20",
     "day20pt2",
+    "day21",
 ]
 
 [profile.dev]

Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "day21"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

day21/Cargo.toml

@@ -0,0 +1,50 @@
+use std::collections::HashSet;
+
+fn take_step(
+    garden: &HashSet<(usize, usize)>,
+    w: usize,
+    h: usize,
+    positions: &HashSet<(usize, usize)>,
+) -> HashSet<(usize, usize)> {
+    let mut new_positions: HashSet<(usize, usize)> = HashSet::new();
+    for pos in positions {
+        if pos.0 > 0 && !garden.contains(&(pos.0 - 1, pos.1)) {
+            new_positions.insert((pos.0 - 1, pos.1));
+        }
+        if pos.0 < w - 1 && !garden.contains(&(pos.0 + 1, pos.1)) {
+            new_positions.insert((pos.0 + 1, pos.1));
+        }
+        if pos.1 > 0 && !garden.contains(&(pos.0, pos.1 - 1)) {
+            new_positions.insert((pos.0, pos.1 - 1));
+        }
+        if pos.1 < h - 1 && !garden.contains(&(pos.0, pos.1 + 1)) {
+            new_positions.insert((pos.0, pos.1 + 1));
+        }
+    }
+    new_positions
+}
+
+fn main() {
+    let mut garden: HashSet<(usize, usize)> = HashSet::new();
+    let mut positions: HashSet<(usize, usize)> = HashSet::new();
+    let mut garden_width: usize = 0;
+    let mut garden_height: usize = 0;
+    for (y, line) in std::io::stdin().lines().map(Result::unwrap).enumerate() {
+        garden_height += 1;
+        for (x, c) in line.chars().enumerate() {
+            if garden_height == 1 {
+                garden_width += 1;
+            }
+            if c == '#' {
+                garden.insert((x, y));
+            }
+            if c == 'S' {
+                positions.insert((x, y));
+            }
+        }
+    }
+    for _ in 0..64 {
+        positions = take_step(&garden, garden_width, garden_height, &positions);
+    }
+    println!("{}", positions.len());
+}