days 7-10

day09/Cargo.lock

@@ -0,0 +1,16 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "day09"
+version = "0.1.0"
+dependencies = [
+ "rustc-hash",
+]
+
+[[package]]
+name = "rustc-hash"
+version = "1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "08d43f7aa6b08d49f382cde6a7982047c3426db949b1424bc4b7ec9ae12c6ce2"

day09/Cargo.toml

@@ -0,0 +1,9 @@
+[package]
+name = "day09"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+rustc-hash = "1.1.0"

day09/src/main.rs

@@ -0,0 +1,73 @@
+use rustc_hash::FxHashSet;
+use std::cmp::Ordering;
+use std::io::{self, BufRead};
+
+fn main() {
+    let lines = io::stdin().lock().lines().map(|l| l.unwrap());
+
+    let mut head = (0, 0);
+    let mut knots: Vec<(isize, isize)> = vec![(0, 0); 9];
+    let mut visited_p1: FxHashSet<(isize, isize)> = FxHashSet::default();
+    let mut visited_p2: FxHashSet<(isize, isize)> = FxHashSet::default();
+
+    visited_p1.insert((0, 0));
+    visited_p2.insert((0, 0));
+
+    for line in lines {
+        let (dir, len) = line.split_once(' ').unwrap();
+        let position = (dir, len.parse::<isize>().unwrap());
+        let mut current;
+
+        for _ in 0..position.1 {
+            step_head(&mut head, position.0);
+            current = head;
+
+            for i in 0..9 {
+                let knot = knots.get_mut(i).unwrap();
+                follow(i, current, knot, &mut visited_p1, &mut visited_p2);
+                current = *knot;
+            }
+        }
+    }
+    println!("P1: {}, P2: {}", visited_p1.len(), visited_p2.len());
+}
+
+fn step_head(head: &mut (isize, isize), dir: &str) {
+    match dir {
+        "L" => head.1 -= 1,
+        "R" => head.1 += 1,
+        "U" => head.0 -= 1,
+        "D" => head.0 += 1,
+        invalid => panic!("invalid direction '{}'", invalid),
+    }
+}
+
+fn follow(
+    idx: usize,
+    head: (isize, isize),
+    tail: &mut (isize, isize),
+    visited_p1: &mut FxHashSet<(isize, isize)>,
+    visited_p2: &mut FxHashSet<(isize, isize)>,
+) {
+    let diffx = (tail.0 - head.0).abs();
+    let diffy = (tail.1 - head.1).abs();
+    if (diffx == 1 || diffx == 0) && (diffy == 1 || diffy == 0) {
+        return;
+    }
+    match tail.0.cmp(&head.0) {
+        Ordering::Greater => tail.0 -= 1,
+        Ordering::Less => tail.0 += 1,
+        _ => (),
+    }
+    match tail.1.cmp(&head.1) {
+        Ordering::Greater => tail.1 -= 1,
+        Ordering::Less => tail.1 += 1,
+        _ => (),
+    }
+    if idx == 0 {
+        visited_p1.insert(*tail);
+    }
+    if idx == 8 {
+        visited_p2.insert(*tail);
+    }
+}