finish day 9

2022/src/day9.rs

@@ -1,4 +1,5 @@
 use std::collections::HashSet;
+use std::fmt::{Display, Formatter};
 use std::str::FromStr;
 
 
@@ -35,14 +36,14 @@ struct Pos {
 #[derive(Debug)]
 struct Rope<const L: usize> {
     knots: [Pos; L],
-    tail_visited: HashSet<Pos>
+    tail_visited: HashSet<Pos>,
 }
 
 impl<const L: usize> Rope<L> {
     fn new() -> Self {
         Rope {
             knots: [Pos {x: 0, y: 0}; L],
-            tail_visited: HashSet::new(),
+            tail_visited: HashSet::new()
         }
     }
 
@@ -72,9 +73,9 @@ impl<const L: usize> Rope<L> {
         let dy = leader.y - follower.y;
 
         // check to make sure that we didn't do anything wrong previously
-        if dx.abs() + dy.abs() > 3
+        if dx.abs() + dy.abs() > 4
-            || dx.abs() == 0 && dy.abs() == 3
+            || dx.abs() == 0 && dy.abs() > 2
-            || dx.abs() == 3 && dy.abs() == 0 
+            || dx.abs() > 2 && dy.abs() == 0 
         {
             panic!("Invalid head and tail positions: {dx}, {dy}");
         }
@@ -98,6 +99,43 @@ impl<const L: usize> Rope<L> {
             follower.y += dy;
             follower.x += dx / 2;
         }
+
+        // offset by 2 in both dimensions
+        if dx.abs() == 2 && dy.abs() == 2 {
+            follower.x += dx / 2;
+            follower.y += dy / 2;
+        }
+    }
+}
+
+
+use std::convert::TryFrom;
+
+impl<const L: usize> Display for Rope<L> {
+    fn fmt(&self, f: &mut Formatter) -> std::fmt::Result {
+        let min_x = self.knots.iter().map(|pos| pos.x).min().unwrap();
+        let max_x = self.knots.iter().map(|pos| pos.x).max().unwrap();
+        let min_y = self.knots.iter().map(|pos| pos.y).min().unwrap();
+        let max_y = self.knots.iter().map(|pos| pos.y).max().unwrap();
+
+        let n_rows = usize::try_from(max_y - min_y + 1).unwrap();
+        let n_cols = usize::try_from(max_x - min_x + 1).unwrap();
+        let mut grid = vec![vec!['.'; n_cols]; n_rows];
+
+        for (i, kt) in self.knots.iter().enumerate() {
+            let rel_x = usize::try_from(kt.x - min_x).unwrap();
+            let rel_y = usize::try_from(max_y - kt.y).unwrap();
+            let tgt = &mut grid[rel_y][rel_x];
+            if *tgt == '.' {
+                *tgt = char::from_digit(i as u32, 10).unwrap();
+            }
+        }
+
+        for row in grid {
+            write!(f, "{}\n", row.iter().collect::<String>())?;
+        }
+
+        Ok(())
     }
 }
 
@@ -117,24 +155,30 @@ fn main() -> Result<(), String> {
         })
         .collect::<Result<Vec<(Direction, isize)>, String>>()?;
 
-    let mut rope = Rope::<10>::new();
+    let mut rope1 = Rope::<2>::new();
-    for (dir, dist) in instructions {
+    for &(dir, dist) in &instructions {
-        rope.do_move(dir, dist)
+        rope1.do_move(dir, dist);
     }
-    println!("{}", rope.tail_visited.len());
+    println!("Part 1: {}", rope1.tail_visited.len());
+
+    let mut rope2 = Rope::<10>::new();
+    for &(dir, dist) in &instructions {
+        rope2.do_move(dir, dist);
+    }
+    println!("Part 2: {}", rope2.tail_visited.len());
 
     Ok(())
 }
 
 
-// const DATA: &'static str = include_str!("../data/day9.txt");
+const DATA: &'static str = include_str!("../data/day9.txt");
-const DATA: &'static str = "
+// const DATA: &'static str = "
-R 5
+// R 5
-U 8
+// U 8
-L 8
+// L 8
-D 3
+// D 3
-R 17
+// R 17
-D 10
+// D 10
-L 25
+// L 25
-U 20
+// U 20
-";
+// ";