Implementation day 3

2020/src/day03.rs

@@ -0,0 +1,60 @@
+use std::io::Read;
+
+use crate::common::read_char_grid;
+use crate::Solution;
+
+#[derive(Default)]
+pub struct Day03;
+
+fn walk(right: usize, down: usize, forrest: &[Vec<u8>]) -> usize {
+    let mut trees = 0;
+    let mut x = 0;
+
+    for line in forrest.iter().step_by(down) {
+        if line[x] == b'#' {
+            trees += 1;
+        }
+
+        x = (x + right) % line.len();
+    }
+
+    trees
+}
+
+impl Solution for Day03 {
+    fn part1(&mut self, input: &mut dyn Read) -> String {
+        let forrest = read_char_grid(input);
+
+        walk(3, 1, &forrest).to_string()
+    }
+
+    fn part2(&mut self, input: &mut dyn Read) -> String {
+        let forrest = read_char_grid(input);
+        let mut product = 1;
+
+        for &(right, down) in &[(1, 1), (3, 1), (5, 1), (7, 1), (1, 2)] {
+            product *= walk(right, down, &forrest);
+        }
+
+        product.to_string()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::test_implementation;
+
+    use super::*;
+
+    const SAMPLE: &[u8] = include_bytes!("../samples/03.txt");
+
+    #[test]
+    fn sample_part1() {
+        test_implementation!(Day03, 1, SAMPLE, 7);
+    }
+
+    #[test]
+    fn sample_part2() {
+        test_implementation!(Day03, 2, SAMPLE, 336);
+    }
+}