Day 14

Author: causal-agent

2017/input/day14.txt

@@ -0,0 +1 @@
+jzgqcdpd

2017/src/bin/day14.rs

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+use std::io::{self, Read};
+
+fn reverse(ring: &mut Vec<u32>, index: usize, len: usize) {
+    for i in 0..(len / 2) {
+        let a = (index + i) % ring.len();
+        let b = (index + len - 1 - i) % ring.len();
+        let x = ring[a];
+        ring[a] = ring[b];
+        ring[b] = x;
+    }
+}
+
+fn hash(input: &str) -> Vec<u8> {
+    let mut ring: Vec<_> = (0..256).collect();
+    let mut index = 0;
+    let mut skip = 0;
+
+    let mut lens: Vec<_> = input.as_bytes().to_vec();
+    lens.extend(&[17, 31, 73, 47, 23]);
+
+    for _ in 0..64 {
+        for len in lens.iter().cloned() {
+            reverse(&mut ring, index, len as usize);
+            index += len as usize + skip;
+            index %= ring.len();
+            skip += 1;
+        }
+    }
+
+    ring.chunks(16)
+        .map(|chunk| chunk.iter().fold(0, |a, b| a ^ b))
+        .map(|x| x as u8)
+        .collect()
+}
+
+fn solve1(input: &str) -> u32 {
+    (0..128)
+        .map(|i| hash(&format!("{}-{}", input, i)))
+        .map(|h| h.into_iter().map(u8::count_ones).sum::<u32>())
+        .sum()
+}
+
+fn main() {
+    let mut input = String::new();
+    io::stdin().read_to_string(&mut input).unwrap();
+
+    println!("Part 1: {}", solve1(input.trim()));
+}
+
+#[test]
+fn part1() {
+    assert_eq!(8108, solve1("flqrgnkx"));
+}