2022 rust day 9

2022/rust/src/solutions/day09.rs

@@ -1,3 +1,4 @@
+#![allow(dead_code)]
 use std::collections::HashSet;
 use crate::utils;
 
@@ -19,45 +20,48 @@ struct Move {
 }
 
 
-fn fix_tail(head: (i32, i32), tail: (i32, i32), direction: &Direction) -> Option<(i32, i32)> {
-    let diff_x = head.0.abs_diff(tail.0);
-    let diff_y = head.1.abs_diff(tail.1);
-    match (diff_y > 1, diff_x > 1, direction) {
-        (true, _, Direction::U) => Some((head.0, head.1 - 1)),
-        (true, _, Direction::D) => Some((head.0, head.1 + 1)),
-        (_, true, Direction::L) => Some((head.0 + 1, head.1)),
-        (_, true, Direction::R) => Some((head.0 - 1, head.1)),
-        (_, _, _) => None,
+#[inline(always)]
+fn fix_tail(head: (i32, i32), tail: (i32, i32)) -> (i32, i32) {
+    let diff_x = tail.0 - head.0;
+    let diff_y = tail.1 - head.1;
+    match (diff_x.abs() > 1, diff_y.abs() > 1) {
+        (true, true) => (head.0 + diff_x.signum(), head.1 + diff_y.signum()),
+        (true, false) => (head.0 + diff_x.signum(), head.1),
+        (false, true) => (head.0, head.1 + diff_y.signum()),
+        _ => tail,
     }
 }
 
-fn tail_visits(data: &[Move]) -> HashSet<(i32, i32)> {
-    let mut set = HashSet::from([(0, 0)]);
-    let mut head = (0, 0);
-    let mut tail = (0, 0);
+fn tail_visits(data: &[Move], knots: &mut [(i32, i32)]) -> HashSet<(i32, i32)> {
+    let mut set = HashSet::from([*knots.last().unwrap()]);
     for m in data {
         for _ in 0..m.units {
-            match m.direction {
-                Direction::U => head = (head.0, head.1 + 1),
-                Direction::D => head = (head.0, head.1 - 1),
-                Direction::L => head = (head.0 - 1, head.1),
-                Direction::R => head = (head.0 + 1, head.1),
-            }
-            if let Some(new) = fix_tail(head, tail, &m.direction) {
-                set.insert(new);
-                tail = new
+            // First move the head
+            let head = knots[0];
+            knots[0] = match m.direction {
+                Direction::U => (head.0, head.1 + 1),
+                Direction::D => (head.0, head.1 - 1),
+                Direction::L => (head.0 - 1, head.1),
+                Direction::R => (head.0 + 1, head.1),
+            };
+            // Second fix all knots sequentially for arbitrary number of knots
+            for idx in 1..knots.len() {
+                knots[idx] = fix_tail(knots[idx-1], knots[idx]);
             }
+            set.insert(*knots.last().unwrap());
         }
     };
     set
 }
 
 fn solve1(data: &[Move]) -> usize {
-    tail_visits(&data).len()
+    let mut knots = [(0, 0); 2];
+    tail_visits(&data, &mut knots).len()
 }
 
-fn solve2(data: &[Move]) -> i32 {
-    2
+fn solve2(data: &[Move]) -> usize {
+    let mut knots = [(0, 0); 10];
+    tail_visits(&data, &mut knots).len()
 }
 
 
@@ -84,17 +88,17 @@ fn parse_data<T: AsRef<str>>(data: &[T]) -> Vec<Move> {
 mod tests {
     use super::*;
 
-    static DATA: &[&str; 8] = &["R 4", "U 4", "L 3", "D 1", "R 4", "D 1", "L 5", "R 2"];
+    static DATA_A: &[&str; 8] = &["R 4", "U 4", "L 3", "D 1", "R 4", "D 1", "L 5", "R 2"];
+    static DATA_B: &[&str; 8] = &["R 5", "U 8", "L 8", "D 3", "R 17", "D 10", "L 25", "U 20"];
 
     #[test]
     fn part1() {
-        let data = parse_data(DATA);
-        assert_eq!(13, solve1(&data));
+        assert_eq!(13, solve1(&parse_data(DATA_A)));
     }
 
     #[test]
     fn part2() {
-        let data = parse_data(DATA);
-        assert_eq!(2, solve2(&data));
+        assert_eq!(1, solve2(&parse_data(DATA_A)));
+        assert_eq!(36, solve2(&parse_data(DATA_B)));
     }
 }