2017 day 14

Author: ictrobot

crates/year2017/src/day10.rs

@@ -1,5 +1,4 @@
-use std::array;
-use utils::md5;
+use crate::knot_hash::{knot_hash_hex, knot_rounds};
 use utils::prelude::*;
 
 /// Implementing a custom hash function.
@@ -21,46 +20,16 @@ impl<'a> Day10<'a> {
             .parse_all(self.input)
             .expect("input invalid for part 1");
 
-        let list = Self::knot_hash(lengths.iter().copied(), 1);
+        let list = knot_rounds(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 hex = knot_hash_hex(self.input.bytes());
 
-        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
+        String::from_utf8(hex.to_vec()).unwrap()
     }
 }
 

crates/year2017/src/day14.rs

@@ -0,0 +1,88 @@
+use crate::knot_hash::knot_hash;
+use utils::bit::BitIterator;
+use utils::prelude::*;
+
+/// Finding connected regions in a hash-derived grid.
+///
+/// This puzzle is a combination of [`Day10`](crate::Day10), which introduced the custom knot hash
+/// function used to create the grid, and [`Day12`](crate::Day12), which also involved finding
+/// connected components.
+#[derive(Clone, Debug)]
+pub struct Day14 {
+    grid: [u128; 128],
+}
+
+impl Day14 {
+    pub fn new(input: &str, _: InputType) -> Result<Self, InputError> {
+        let mut grid = [0u128; 128];
+
+        let mut buf = Vec::with_capacity(input.len() + 4);
+        buf.extend_from_slice(input.as_bytes());
+        buf.push(b'-');
+
+        for (i, row) in grid.iter_mut().enumerate() {
+            buf.truncate(input.len() + 1);
+            if i < 10 {
+                buf.push(b'0' + (i as u8));
+            } else if i < 100 {
+                buf.push(b'0' + ((i / 10) as u8));
+                buf.push(b'0' + ((i % 10) as u8));
+            } else {
+                buf.push(b'0' + ((i / 100) as u8));
+                buf.push(b'0' + (((i / 10) % 10) as u8));
+                buf.push(b'0' + ((i % 10) as u8));
+            }
+
+            let hash = knot_hash(buf.iter().copied());
+            *row = u128::from_be_bytes(hash);
+        }
+
+        Ok(Day14 { grid })
+    }
+
+    #[must_use]
+    pub fn part1(&self) -> u32 {
+        self.grid.iter().map(|x| x.count_ones()).sum()
+    }
+
+    #[must_use]
+    pub fn part2(&self) -> u32 {
+        let mut regions = 0;
+        let mut visited = [0u128; 128];
+
+        for (r, &row) in self.grid.iter().enumerate() {
+            for (_, bit) in BitIterator::ones(row) {
+                if visited[r] & bit == 0 {
+                    regions += 1;
+                    self.visit(&mut visited, r, bit)
+                }
+            }
+        }
+
+        regions
+    }
+
+    fn visit(&self, visited: &mut [u128; 128], r: usize, bit: u128) {
+        visited[r] |= bit;
+
+        if r > 0 && self.grid[r - 1] & bit != 0 && visited[r - 1] & bit == 0 {
+            self.visit(visited, r - 1, bit);
+        }
+        if r < 127 && self.grid[r + 1] & bit != 0 && visited[r + 1] & bit == 0 {
+            self.visit(visited, r + 1, bit);
+        }
+
+        let left = bit << 1;
+        if left != 0 && self.grid[r] & left != 0 && visited[r] & left == 0 {
+            self.visit(visited, r, left);
+        }
+        let right = bit >> 1;
+        if right != 0 && self.grid[r] & right != 0 && visited[r] & right == 0 {
+            self.visit(visited, r, right);
+        }
+    }
+}
+
+examples!(Day14 -> (u32, u32) [
+    {input: "flqrgnkx", part1: 8108, part2: 1242},
+]);

crates/year2017/src/knot_hash.rs

@@ -0,0 +1,45 @@
+//! Knot Hash implementation.
+//!
+//! See [`Day10`](crate::Day10) and [`Day14`](crate::Day14).
+
+use std::array;
+use utils::md5;
+
+#[inline]
+pub(crate) fn knot_rounds(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
+}
+
+#[inline]
+pub(crate) fn knot_hash(lengths: impl Iterator<Item = u8> + Clone) -> [u8; 16] {
+    let sparse = knot_rounds(lengths.chain([17, 31, 73, 47, 23]), 64);
+
+    array::from_fn(|i| {
+        sparse[16 * i..16 * (i + 1)]
+            .iter()
+            .fold(0, |acc, x| acc ^ x)
+    })
+}
+
+#[inline]
+pub(crate) fn knot_hash_hex(lengths: impl Iterator<Item = u8> + Clone) -> [u8; 32] {
+    let hash = knot_hash(lengths);
+
+    md5::to_hex(array::from_fn(|i| {
+        u32::from_be_bytes(hash[4 * i..4 * (i + 1)].try_into().unwrap())
+    }))
+}

crates/year2017/src/lib.rs

@@ -1,6 +1,8 @@
 #![doc = include_str!("../README.md")]
 #![cfg_attr(not(feature = "unsafe"), forbid(unsafe_code))]
 
+mod knot_hash;
+
 utils::year!(2017 => year2017, ${
     1 => day01::Day01<'_>,
     2 => day02::Day02,
@@ -15,4 +17,5 @@ utils::year!(2017 => year2017, ${
     11 => day11::Day11,
     12 => day12::Day12,
     13 => day13::Day13,
+    14 => day14::Day14,
 });