Rust Day 3

rust/.vscode/settings.json

@@ -0,0 +1,3 @@
+{
+  "rust-analyzer.showUnlinkedFileNotification": false
+}

rust/Cargo.lock

@@ -4,4 +4,4 @@ version = 3
 
 [[package]]
 name = "advent-of-code"
-version = "20.1.2"
+version = "20.3.2"

rust/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "advent-of-code"
-version = "20.1.2"
+version = "20.3.2"
 edition = "2021"
 resolver = "2"
 
@@ -30,3 +30,7 @@ path = "src/day01/main.rs"
 [[bin]]
 name = "day02"
 path = "src/day02/main.rs"
+
+[[bin]]
+name = "day03"
+path = "src/day03/main.rs"

rust/src/day02/main.rs

@@ -21,7 +21,7 @@ impl FromStr for Password {
     type Err = ParseError;
 
     fn from_str(line: &str) -> Result<Self, Self::Err> {
-        let parts = line.split(" ").collect::<Vec<_>>();
+        let parts = line.split(' ').collect::<Vec<_>>();
 
         if parts.len() != 3 {
             return Err(ParseError(line.into()));
@@ -30,7 +30,7 @@ impl FromStr for Password {
         let first_num = nums_iter.next().unwrap();
         let second_num = nums_iter.next().unwrap();
 
-        let letter = parts[1].chars().nth(0).unwrap();
+        let letter = parts[1].chars().next().unwrap();
         let password = parts[2].into();
 
         Ok(Password {

rust/src/day03/input.txt

@@ -0,0 +1,323 @@
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rust/src/day03/main.rs

@@ -0,0 +1,45 @@
+const INPUT: &str = include_str!("input.txt");
+
+mod part_1;
+use part_1::part_1;
+mod part_2;
+use part_2::part_2;
+
+pub struct ParsedInput {
+    pub field: Vec<Vec<Spot>>,
+    pub width: usize,
+    pub height: usize,
+}
+pub enum Spot {
+    Empty,
+    Tree,
+}
+impl From<&u8> for Spot {
+    fn from(value: &u8) -> Self {
+        match value {
+            b'.' => Self::Empty,
+            b'#' => Self::Tree,
+            _ => unreachable!(),
+        }
+    }
+}
+
+pub fn parse_input(input: &'static str) -> ParsedInput {
+    let field = input
+        .lines()
+        .map(|line| line.as_bytes().iter().map(Spot::from).collect())
+        .collect::<Vec<Vec<_>>>();
+    let height = field.len();
+    let width = field[0].len();
+    ParsedInput {
+        field,
+        width,
+        height,
+    }
+}
+
+pub fn main() {
+    let input = parse_input(INPUT);
+    part_1(&input);
+    part_2(&input);
+}

rust/src/day03/part_1.rs

@@ -0,0 +1,27 @@
+use crate::{ParsedInput, Spot};
+
+pub(crate) fn part_1(input: &ParsedInput) -> u64 {
+    let mut result = 0;
+    for y in 0..input.height {
+        let x = (y * 3) % input.width;
+        if matches!(input.field[y][x], Spot::Tree) {
+            result += 1;
+        }
+    }
+    result
+}
+
+#[cfg(test)]
+mod tests {
+    const SAMPLE_INPUT: &str = include_str!("sample_input.txt");
+
+    #[test]
+    fn test_with_sample_solution() {
+        assert_eq!(super::part_1(&crate::parse_input(SAMPLE_INPUT)), 7);
+    }
+
+    #[test]
+    fn test_with_solution() {
+        assert_eq!(super::part_1(&crate::parse_input(crate::INPUT)), 187);
+    }
+}

rust/src/day03/part_2.rs

@@ -0,0 +1,34 @@
+use crate::{ParsedInput, Spot};
+
+pub(crate) fn part_2(input: &ParsedInput) -> u64 {
+    let mut result = 1;
+    for (dx, dy) in [(1, 1), (3, 1), (5, 1), (7, 1), (1, 2)] {
+        let mut count = 0;
+        let mut x = 0;
+        let mut y = 0;
+        while y < input.height {
+            if matches!(input.field[y][x], Spot::Tree) {
+                count += 1;
+            }
+            x = (x + dx) % input.width;
+            y += dy;
+        }
+        result *= count;
+    }
+    result
+}
+
+#[cfg(test)]
+mod tests {
+    const SAMPLE_INPUT: &str = include_str!("sample_input.txt");
+
+    #[test]
+    fn test_with_sample_solution() {
+        assert_eq!(super::part_2(&crate::parse_input(SAMPLE_INPUT)), 336);
+    }
+
+    #[test]
+    fn test_with_solution() {
+        assert_eq!(super::part_2(&crate::parse_input(crate::INPUT)), 4723283400);
+    }
+}

rust/src/day03/sample_input.txt

@@ -0,0 +1,11 @@
+..##.......
+#...#...#..
+.#....#..#.
+..#.#...#.#
+.#...##..#.
+..#.##.....
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+.#........#
+#.##...#...
+#...##....#
+.#..#...#.#