1 files changed, 74 insertions, 0 deletions
diff --git a/2020/day03/src/main.rs b/2020/day03/src/main.rs
new file mode 100644
index 0000000..6e74f74
--- /dev/null
+++ b/2020/day03/src/main.rs
@@ -0,0 +1,74 @@
+fn slide(lines: Vec<Vec<char>>, vx: i32, vy: i32) -> i32 {
+    let mut x: i32 = 0;
+    let mut y: i32 = 0;
+    let mut hits: i32 = 0;
+    loop {
+        if lines[y as usize][x as usize] == '#' {
+            hits += 1;
+        }
+        x += vx;
+        y += vy;
+        if y as usize >= lines.len() {
+            break;
+        }
+        if x as usize >= lines[y as usize].len() {
+            x -= lines[y as usize].len() as i32;
+        }
+    }
+    hits
+}
+
+fn slide_everywhere(lines: Vec<Vec<char>>) -> i32 {
+    let mut hits: i32 = 1;
+    for (vx, vy) in vec![(1, 1), (3, 1), (5, 1), (7, 1), (1, 2)] {
+        hits *= slide(lines.clone(), vx, vy);
+    }
+    hits
+}
+
+fn main() {
+    let lines: Vec<Vec<char>> = include_str!("../input0.txt")
+        .trim()
+        .split("\n")
+        .map(|s| s.chars().collect())
+        .collect();
+    let hits = slide(lines.clone(), 3, 1);
+    println!("hits: {}", hits);
+    let hits_everything = slide_everywhere(lines.clone());
+    println!("hits on the five paths: {}", hits_everything);
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::*;
+
+    #[test]
+    fn small_input() {
+        let lines: Vec<Vec<char>> = include_str!("../test0.txt")
+            .trim()
+            .split("\n")
+            .map(|s| s.chars().collect())
+            .collect();
+        assert_eq!(slide(lines, 3, 1), 7);
+    }
+
+    #[test]
+    fn big_input() {
+        let lines: Vec<Vec<char>> = include_str!("../input0.txt")
+            .trim()
+            .split("\n")
+            .map(|s| s.chars().collect())
+            .collect();
+        assert_eq!(slide(lines, 3, 1), 220);
+    }
+
+    #[test]
+    fn small_input_all_slopes() {
+        let lines: Vec<Vec<char>> = include_str!("../test0.txt")
+            .trim()
+            .split("\n")
+            .map(|s| s.chars().collect())
+            .collect();
+        assert_eq!(slide_everywhere(lines), 336);
+    }
+}