do day 9

2022/input/day_9_sample.txt

@@ -0,0 +1,8 @@
+R 5
+U 8
+L 8
+D 3
+R 17
+D 10
+L 25
+U 20

2022/src/day_9.rs

@@ -0,0 +1,141 @@
+use std::collections::HashSet;
+use Direction::*;
+
+#[derive(Debug)]
+enum Direction {
+    L,
+    R,
+    U,
+    D,
+}
+
+#[derive(Debug)]
+struct Instruction {
+    direction: Direction,
+    steps: i32,
+}
+
+#[derive(Debug, PartialEq, Eq, Hash, Clone, Copy)]
+struct Location {
+    x: i32,
+    y: i32,
+}
+
+type Data = Vec<Instruction>;
+type Output = usize;
+fn parse(input: &str) -> Data {
+    input
+        .lines()
+        .map(|line| {
+            let (direction, steps) = line.split_once(' ').unwrap();
+            Instruction {
+                direction: match direction {
+                    "L" => L,
+                    "R" => R,
+                    "D" => D,
+                    "U" => U,
+                    _ => panic!("expected L, R, D, or U. got {}", direction),
+                },
+                steps: steps.parse().unwrap(),
+            }
+        })
+        .collect()
+}
+fn part_one(data: Data) -> Output {
+    let mut locations = HashSet::<Location>::new();
+    let mut head = Location { x: 0, y: 0 };
+    let mut tail = head;
+    locations.insert(tail);
+    for instr in data {
+        for _ in 0..instr.steps {
+            // println!("{:?}", tail);
+            match instr.direction {
+                L => {
+                    head.x -= 1;
+                    if tail.x == head.x + 2 {
+                        tail.x = head.x + 1;
+                        tail.y = head.y;
+                    }
+                }
+                R => {
+                    head.x += 1;
+                    if tail.x == head.x - 2 {
+                        tail.x = head.x - 1;
+                        tail.y = head.y;
+                    }
+                }
+                U => {
+                    head.y += 1;
+                    if tail.y + 2 == head.y {
+                        tail.x = head.x;
+                        tail.y = head.y - 1;
+                    }
+                }
+                D => {
+                    head.y -= 1;
+                    if tail.y == head.y + 2 {
+                        tail.x = head.x;
+                        tail.y = head.y + 1;
+                    }
+                }
+            }
+            locations.insert(tail);
+        }
+    }
+    locations.len()
+}
+fn part_two(data: Data) -> Output {
+    let mut locations = HashSet::<Location>::new();
+    let mut rope = [Location { x: 0, y: 0 }; 10];
+    locations.insert(rope[9]);
+    for instr in data {
+        for _ in 0..instr.steps {
+            match instr.direction {
+                L => {
+                    rope[0].x -= 1;
+                }
+                R => {
+                    rope[0].x += 1;
+                }
+                U => {
+                    rope[0].y += 1;
+                }
+                D => {
+                    rope[0].y -= 1;
+                }
+            }
+            for i in 1..rope.len() {
+                if rope[i].x.abs_diff(rope[i - 1].x) == 2 && rope[i].y.abs_diff(rope[i - 1].y) == 2
+                {
+                    rope[i] = Location {
+                        x: rope[i - 1].x + if rope[i - 1].x > rope[i].x { -1 } else { 1 },
+                        y: rope[i - 1].y + if rope[i - 1].y > rope[i].y { -1 } else { 1 },
+                    };
+                } else if rope[i].x >= rope[i - 1].x + 2 {
+                    rope[i].x = rope[i - 1].x + 1;
+                    rope[i].y = rope[i - 1].y;
+                } else if rope[i].y >= rope[i - 1].y + 2 {
+                    rope[i].x = rope[i - 1].x;
+                    rope[i].y = rope[i - 1].y + 1;
+                } else if rope[i].y <= rope[i - 1].y - 2 {
+                    rope[i].x = rope[i - 1].x;
+                    rope[i].y = rope[i - 1].y - 1;
+                } else if rope[i].x <= rope[i - 1].x - 2 {
+                    rope[i].x = rope[i - 1].x - 1;
+                    rope[i].y = rope[i - 1].y;
+                }
+            }
+            locations.insert(rope[rope.len() - 1]);
+        }
+    }
+    locations.len()
+}
+
+advent_of_code_macro::generate_tests!(
+    day 9,
+    parse,
+    part_one,
+    part_two,
+    sample tests [88, 36],
+    star tests [6337, 2455]
+);

2022/src/lib.rs

@@ -7,3 +7,4 @@ mod day_5;
 mod day_6;
 mod day_7;
 mod day_8;
+mod day_9;