Day 09

src/day09/mod.rs

@@ -1,18 +1,101 @@
 use crate::read;
 use itertools::Itertools;
+use std::collections::HashSet;
+
+#[derive(Debug, PartialEq, Eq, Default, Clone, Copy, Hash)]
+struct Position {
+    pub x: i32,
+    pub y: i32,
+}
+
+impl Position {
+    pub fn to_right(&self, count: i32) -> Self {
+        Self {
+            x: self.x + count,
+            y: self.y,
+        }
+    }
+    pub fn to_left(&self, count: i32) -> Self {
+        Self {
+            x: self.x - count,
+            y: self.y,
+        }
+    }
+    pub fn to_up(&self, count: i32) -> Self {
+        Self {
+            x: self.x,
+            y: self.y - count,
+        }
+    }
+    pub fn to_down(&self, count: i32) -> Self {
+        Self {
+            x: self.x,
+            y: self.y + count,
+        }
+    }
+
+    pub fn follow_head(&self, head: &Position) -> Self {
+        if head.x == self.x && head.y > self.y + 1 {
+            self.to_down(1)
+        } else if head.x == self.x && head.y < self.y - 1 {
+            self.to_up(1)
+        } else if head.x > self.x + 1 && head.y == self.y {
+            self.to_right(1)
+        } else if head.x < self.x - 1 && head.y == self.y {
+            self.to_left(1)
+        } else if (head.x - self.x).abs() == 1 && (head.y - self.y).abs() == 1 {
+            *self
+        } else if head.x < self.x && head.y < self.y {
+            self.to_left(1).to_up(1)
+        } else if head.x > self.x && head.y < self.y {
+            self.to_right(1).to_up(1)
+        } else if head.x > self.x && head.y > self.y {
+            self.to_right(1).to_down(1)
+        } else if head.x < self.x && head.y > self.y {
+            self.to_left(1).to_down(1)
+        } else {
+            *self
+        }
+    }
+}
 
 pub fn run() {
-    let input = read("08");
-    let lines = input.lines();
-    for line in lines {}
-
     #[cfg(feature = "part1")]
     {
-        println!("Day 9, Part 01: {}", "TODO");
+        println!("Day 9, Part 01: {}", simulate(2));
     }
 
     #[cfg(feature = "part2")]
     {
-        println!("Day 9, Part 02: {}", "TODO");
+        println!("Day 9, Part 02: {}", simulate(10));
     }
 }
+pub fn simulate(num_knots: usize) -> usize {
+    let mut visited: HashSet<Position> = HashSet::new();
+    let mut knots = vec![Position::default(); num_knots];
+
+    let input = read("09");
+    let lines = input.lines();
+    for line in lines {
+        if line.is_empty() {
+            continue;
+        }
+        let (dir, count) = line.split_once(' ').unwrap();
+        let count = count.parse().unwrap();
+        for _c in 0..count {
+            knots[0] = match dir {
+                "R" => knots[0].to_right(1),
+                "U" => knots[0].to_up(1),
+                "L" => knots[0].to_left(1),
+                "D" => knots[0].to_down(1),
+                _ => unreachable!(),
+            };
+            for i in 1..knots.len() {
+                knots[i] = knots[i].follow_head(&knots[i - 1]);
+            }
+
+            visited.insert(*knots.last().unwrap());
+        }
+    }
+    visited.len()
+}