2017 day 10

Author: ictrobot

crates/aoc/src/main.rs

@@ -35,8 +35,9 @@ fn main() {
         exit(1);
     }
 
-    println!("Puzzle  │ Part 1                      │ Part 2                      │ Time      ");
-    println!("────────┼─────────────────────────────┼─────────────────────────────┼───────────");
+    // FIXME support 80 character wide output (without time?)
+    println!("Puzzle  │ Part 1                           │ Part 2                           │ Time      ");
+    println!("────────┼──────────────────────────────────┼──────────────────────────────────┼───────────");
 
     let mut total = Duration::default();
     for (year, day, f) in puzzles {
@@ -56,8 +57,8 @@ fn main() {
 
                 // Hack to treat "🎄" as two characters wide
                 // ("🎄" is 1 wide in Unicode 8 but 2 wide in Unicode 9+)
-                let part1_width = if part1 == "🎄" { 26 } else { 27 };
-                let part2_width = if part2 == "🎄" { 26 } else { 27 };
+                let part1_width = if part1 == "🎄" { 31 } else { 32 };
+                let part2_width = if part2 == "🎄" { 31 } else { 32 };
 
                 println!(
                     "{year:#} {day:#} │ {part1:<part1_width$} │ {part2:<part2_width$} │ {}",
@@ -71,9 +72,11 @@ fn main() {
         }
     }
 
-    println!("────────┴─────────────────────────────┴─────────────────────────────┼───────────");
     println!(
-        "                                                                    │ {}",
+        "────────┴──────────────────────────────────┴──────────────────────────────────┼───────────"
+    );
+    println!(
+        "                                                                              │ {}",
         format_duration(total),
     );
 }

crates/year2017/src/day10.rs

@@ -0,0 +1,72 @@
+use std::array;
+use utils::md5;
+use utils::prelude::*;
+
+/// Implementing a custom hash function.
+#[derive(Clone, Debug)]
+pub struct Day10<'a> {
+    input: &'a str,
+}
+
+impl<'a> Day10<'a> {
+    pub fn new(input: &'a str, _: InputType) -> Result<Self, InputError> {
+        // Parts 1 and 2 expect different input
+        Ok(Self { input })
+    }
+
+    #[must_use]
+    pub fn part1(&self) -> u32 {
+        let lengths = parser::u8()
+            .with_suffix(b','.optional())
+            .parse_all(self.input)
+            .expect("input invalid for part 1");
+
+        let list = Self::knot_hash(lengths.iter().copied(), 1);
+
+        list[0] as u32 * list[1] as u32
+    }
+
+    #[must_use]
+    pub fn part2(&self) -> String {
+        let lengths = self.input.bytes().chain([17, 31, 73, 47, 23]);
+
+        let sparse = Self::knot_hash(lengths, 64);
+
+        let dense: [u8; 16] = array::from_fn(|i| {
+            sparse[16 * i..16 * (i + 1)]
+                .iter()
+                .fold(0, |acc, x| acc ^ x)
+        });
+
+        let dense_hex = md5::to_hex(array::from_fn(|i| {
+            u32::from_be_bytes(dense[4 * i..4 * (i + 1)].try_into().unwrap())
+        }));
+
+        String::from_utf8(dense_hex.to_vec()).unwrap()
+    }
+
+    fn knot_hash(lengths: impl Iterator<Item = u8> + Clone, rounds: u32) -> [u8; 256] {
+        let mut list = array::from_fn(|i| i as u8);
+        let mut position = 0;
+        let mut skip = 0;
+
+        for _ in 0..rounds {
+            for length in lengths.clone() {
+                list[0..length as usize].reverse();
+                list.rotate_left((length as usize + skip) % 256);
+                position = (position + length as usize + skip) % 256;
+                skip += 1;
+            }
+        }
+
+        list.rotate_right(position);
+        list
+    }
+}
+
+examples!(Day10<'_> -> (u32, &'static str) [
+    {input: "", part2: "a2582a3a0e66e6e86e3812dcb672a272"},
+    {input: "AoC 2017", part2: "33efeb34ea91902bb2f59c9920caa6cd"},
+    {input: "1,2,3", part2: "3efbe78a8d82f29979031a4aa0b16a9d"},
+    {input: "1,2,4", part2: "63960835bcdc130f0b66d7ff4f6a5a8e"},
+]);

crates/year2017/src/lib.rs

@@ -11,4 +11,5 @@ utils::year!(2017 => year2017, ${
     7 => day07::Day07<'_>,
     8 => day08::Day08,
     9 => day09::Day09,
+    10 => day10::Day10<'_>,
 });