Implementation day 12

2020/inputs/12.txt

@@ -0,0 +1,784 @@
+R90
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+F60

2020/samples/12.txt

@@ -0,0 +1,5 @@
+F10
+N3
+F7
+R90
+F11

2020/src/day12.rs

@@ -1,12 +1,107 @@
 use std::io::Read;
 
+use crate::common::Lines;
 use crate::Solution;
 
+// Rotate clockwise
+fn rotate(amount: i32, (x, y): (i32, i32)) -> (i32, i32) {
+    debug_assert!(amount >= 0);
+    debug_assert_eq!(amount % 90, 0);
+
+    match amount {
+        90 => (y, -x),
+        180 => (-x, -y),
+        270 => (-y, x),
+        360 => (x, y),
+        _ => panic!("Invalid rotate manouvre {}", amount),
+    }
+}
+
 #[derive(Default)]
 pub struct Day12;
 
 impl Solution for Day12 {
-    fn part1(&mut self, _input: &mut dyn Read) -> String {
+    fn part1(&mut self, input: &mut dyn Read) -> String {
-        todo!()
+        let mut x = 0;
+        let mut y = 0;
+        let mut v = (1, 0);
+
+        for line in Lines::new(input) {
+            let dir = &line[0..1];
+            let amount: i32 = line[1..].parse().unwrap();
+
+            match dir {
+                "N" => y += amount,
+                "E" => x += amount,
+                "S" => y -= amount,
+                "W" => x -= amount,
+                "F" => {
+                    let (dx, dy) = v;
+
+                    x += amount * dx;
+                    y += amount * dy;
+                }
+                "R" => v = rotate(amount, v),
+                "L" => v = rotate(360 - amount, v),
+                _ => panic!("Invalid direction '{}'", dir),
+            };
+        }
+
+        (x.abs() + y.abs()).to_string()
+    }
+
+    fn part2(&mut self, input: &mut dyn Read) -> String {
+        let mut x = 0;
+        let mut y = 0;
+        let mut wx = 10;
+        let mut wy = 1;
+
+        for line in Lines::new(input) {
+            let dir = &line[0..1];
+            let amount: i32 = line[1..].parse().unwrap();
+
+            match dir {
+                "N" => wy += amount,
+                "E" => wx += amount,
+                "S" => wy -= amount,
+                "W" => wx -= amount,
+                "F" => {
+                    x += wx * amount;
+                    y += wy * amount;
+                }
+                "R" => {
+                    let v = rotate(amount, (wx, wy));
+                    wx = v.0;
+                    wy = v.1;
+                }
+                "L" => {
+                    let v = rotate(360 - amount, (wx, wy));
+                    wx = v.0;
+                    wy = v.1;
+                }
+                _ => panic!("Invalid direction '{}'", dir),
+            };
+        }
+
+        (x.abs() + y.abs()).to_string()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::test_implementation;
+
+    use super::*;
+
+    const SAMPLE: &[u8] = include_bytes!("../samples/12.txt");
+
+    #[test]
+    fn sample_part1() {
+        test_implementation!(Day12, 1, SAMPLE, 25);
+    }
+
+    #[test]
+    fn sample_part2() {
+        test_implementation!(Day12, 2, SAMPLE, 286);
     }
 }