add day 9, part 2

day09/common.rs

@@ -25,15 +25,14 @@ enum Direction {
 }
 
 #[derive(Debug, Clone, Copy)]
-pub struct RopeState {
-    head_pos: (isize, isize),
-    tail_pos: (isize, isize),
+pub struct RopeState<const LEN: usize> {
+    knots: [(isize, isize); LEN],
 }
 
-pub struct RopeStates {
+pub struct RopeStates<const LEN: usize> {
     direction: Direction,
     count: isize,
-    state: RopeState,
+    state: RopeState<LEN>,
 }
 
 impl FromStr for Direction {
@@ -50,63 +49,65 @@ impl FromStr for Direction {
     }
 }
 
-impl RopeState {
+impl<const LEN: usize> RopeState<LEN> {
     pub fn new() -> Self {
-        RopeState {
-            head_pos: (0, 0),
-            tail_pos: (0, 0),
+        Self {
+            knots: [(0, 0); LEN],
         }
     }
 
     pub fn head_pos(&self) -> (isize, isize) {
-        self.head_pos
+        self.knots[0]
     }
 
     pub fn tail_pos(&self) -> (isize, isize) {
-        self.tail_pos
+        self.knots[LEN - 1]
     }
 
-    fn adjust_tail(&mut self) {
-        let x_diff = self.head_pos.0.abs_diff(self.tail_pos.0);
-        let y_diff = self.head_pos.1.abs_diff(self.tail_pos.1);
+    fn adjust_knot(&mut self, index: usize) {
+        let x_diff = self.knots[index - 1].0.abs_diff(self.knots[index].0);
+        let y_diff = self.knots[index - 1].1.abs_diff(self.knots[index].1);
         let (move_x, move_y) = match (x_diff, y_diff) {
             (2, 0) => (true, false),
             (2, 1) => (true, true),
             (0, 2) => (false, true),
             (1, 2) => (true, true),
+            (2, 2) => (true, true),
             _ => (false, false),
         };
         if move_x {
-            match (self.head_pos.0, self.tail_pos.0) {
-                (h, t) if { h > t } => self.tail_pos.0 += 1,
-                (h, t) if { h < t } => self.tail_pos.0 -= 1,
+            match (self.knots[index - 1].0, self.knots[index].0) {
+                (h, t) if { h > t } => self.knots[index].0 += 1,
+                (h, t) if { h < t } => self.knots[index].0 -= 1,
                 _ => (),
             }
         }
         if move_y {
-            match (self.head_pos.1, self.tail_pos.1) {
-                (h, t) if { h > t } => self.tail_pos.1 += 1,
-                (h, t) if { h < t } => self.tail_pos.1 -= 1,
+            match (self.knots[index - 1].1, self.knots[index].1) {
+                (h, t) if { h > t } => self.knots[index].1 += 1,
+                (h, t) if { h < t } => self.knots[index].1 -= 1,
                 _ => (),
             }
         }
     }
 
-    fn move_head(&mut self, direction: Direction) -> Result<RopeState, &'static str> {
+    fn move_head(&mut self, direction: Direction) -> Result<RopeState<LEN>, &'static str> {
         const ERROR: &'static str = "invalid move";
         match direction {
-            Direction::Up => self.head_pos.1 = self.head_pos.1.checked_add(1).ok_or(ERROR)?,
-            Direction::Right => self.head_pos.0 = self.head_pos.0.checked_add(1).ok_or(ERROR)?,
-            Direction::Down => self.head_pos.1 = self.head_pos.1.checked_sub(1).ok_or(ERROR)?,
-            Direction::Left => self.head_pos.0 = self.head_pos.0.checked_sub(1).ok_or(ERROR)?,
+            Direction::Up => self.knots[0].1 = self.knots[0].1.checked_add(1).ok_or(ERROR)?,
+            Direction::Right => self.knots[0].0 = self.knots[0].0.checked_add(1).ok_or(ERROR)?,
+            Direction::Down => self.knots[0].1 = self.knots[0].1.checked_sub(1).ok_or(ERROR)?,
+            Direction::Left => self.knots[0].0 = self.knots[0].0.checked_sub(1).ok_or(ERROR)?,
+        }
+        for i in 1..LEN {
+            self.adjust_knot(i);
         }
-        self.adjust_tail();
         Ok(*self)
     }
 }
 
-impl Iterator for RopeStates {
-    type Item = Result<RopeState, &'static str>;
+impl<const LEN: usize> Iterator for RopeStates<LEN> {
+    type Item = Result<RopeState<LEN>, &'static str>;
 
     fn next(&mut self) -> Option<Self::Item> {
         if self.count == 0 {
@@ -133,7 +134,7 @@ impl Iterator for RopeStates {
     }
 }
 
-pub fn rope_states() -> RopeStates {
+pub fn rope_states<const LEN: usize>() -> RopeStates<LEN> {
     RopeStates {
         direction: Direction::Up,
         count: 0,

day09/part1.rs

@@ -20,8 +20,9 @@ pub mod common;
 use std::collections::HashSet;
 
 fn main() -> Result<(), &'static str> {
-    let tail_positions: Result<HashSet<(isize, isize)>, _> =
-        common::rope_states().map(|s| Ok(s?.tail_pos())).collect();
+    let tail_positions: Result<HashSet<(isize, isize)>, _> = common::rope_states::<2>()
+        .map(|s| Ok(s?.tail_pos()))
+        .collect();
     println!("{}", tail_positions?.len());
     Ok(())
 }

day09/part2.rs

@@ -0,0 +1,28 @@
+// Copyright 2022 Christian Ulrich
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+//
+// usage: ./part2 < input
+
+pub mod common;
+
+use std::collections::HashSet;
+
+fn main() -> Result<(), &'static str> {
+    let tail_positions: Result<HashSet<(isize, isize)>, _> = common::rope_states::<10>()
+        .map(|s| Ok(s?.tail_pos()))
+        .collect();
+    println!("{}", tail_positions?.len());
+    Ok(())
+}