day12

src/day12.rs

@@ -0,0 +1,137 @@
+use aoc_runner_derive::{aoc, aoc_generator};
+
+use Instruction::*;
+use itertools::Itertools;
+
+#[derive(Debug)]
+enum Instruction {
+    MoveNorth(i32),
+    MoveSouth(i32),
+    MoveEast(i32),
+    MoveWest(i32),
+    TurnLeft(i32),
+    TurnRight(i32),
+    MoveForward(i32)
+}
+
+impl From<(char, i32)> for Instruction {
+    fn from(value: (char, i32)) -> Self {
+        match value {
+            (i, v) if i == 'N' => MoveNorth(v),
+            (i, v) if i == 'S' => MoveSouth(v),
+            (i, v) if i == 'E' => MoveEast(v),
+            (i, v) if i == 'W' => MoveWest(v),
+            (i, v) if i == 'L' => TurnLeft(v),
+            (i, v) if i == 'R' => TurnRight(v),
+            (i, v) if i == 'F' => MoveForward(v),
+            _ => unreachable!()
+        }
+    }
+}
+
+#[aoc_generator(day12)]
+fn parse(input: &str) -> Vec<Instruction> {
+    input
+    .lines()
+    .map(|line| {
+        (line.chars().next().unwrap(), line[1..].parse::<i32>().unwrap()).into()
+    })
+    .collect_vec()
+}
+
+const DIR_POS_MODIFIER: [(i32, i32); 4] = [(1, 0), (0, -1), (-1, 0), (0, 1)];
+
+#[aoc(day12, part1)]
+fn part1(input: &Vec<Instruction>) -> i32 {
+    let mut x = 0;
+    let mut y = 0;
+    let mut direction = 0; // 0 is east, thus 90 is south, 180 is west, and 270 is north
+
+    for instr in input {
+        match instr {
+            MoveNorth(val) => y += val,
+            MoveSouth(val) => y -= val,
+            MoveEast(val) => x += val,
+            MoveWest(val) => x -= val,
+            TurnLeft(val) => {
+                direction -= val;
+                if direction < 0 {
+                    direction += 360;
+                }
+            },
+            TurnRight(val) => {
+                direction += val;
+                if direction >= 360 {
+                    direction -= 360
+                }
+            },
+            MoveForward(val) => {
+                let (xmod, ymod) = DIR_POS_MODIFIER[(direction / 90) as usize];
+                x += xmod * val;
+                y += ymod * val;
+            },
+        }
+    }
+
+    x.abs() + y.abs()
+}
+
+#[aoc(day12, part2)]
+fn part2(input: &Vec<Instruction>) -> i32 {
+    let mut way_x = 10;
+    let mut way_y = 1;
+
+    let mut ship_x: i32 = 0;
+    let mut ship_y: i32 = 0;
+
+    for instr in input {
+        match instr {
+            MoveNorth(val) => way_y += val,
+            MoveSouth(val) => way_y -= val,
+            MoveEast(val) => way_x += val,
+            MoveWest(val) => way_x -= val,
+            TurnLeft(val) => {
+                for _ in 0..(val / 90) {
+                    let tmp = way_y;
+                    way_y = way_x;
+                    way_x = -tmp;
+                }
+            },
+            TurnRight(val) => {
+                for _ in 0..(val / 90) {
+                    let tmp = way_y;
+                    way_y = -way_x;
+                    way_x = tmp;
+                }
+            },
+            MoveForward(val) => {
+                ship_x += way_x * val;
+                ship_y += way_y * val;
+            },
+        }
+    }
+
+    ship_x.abs() + ship_y.abs()
+}
+
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+const EX: &str = r"F10
+N3
+F7
+R90
+F11";
+
+    #[test]
+    fn part1_example() {
+        assert_eq!(part1(&parse(EX)), 25);
+    }
+
+    #[test]
+    fn part2_example() {
+        assert_eq!(part2(&parse(EX)), 286);
+    }
+}

src/lib.rs

@@ -1,3 +1,4 @@
+mod day12;
 mod day10;
 mod day9;
 mod day8;