Day 10, part 2

1 files changed, 32 insertions, 0 deletions

diff --git a/2017/src/bin/day10.rs b/2017/src/bin/day10.rs
index af90961..615f468 100644
--- a/2017/src/bin/day10.rs
+++ b/2017/src/bin/day10.rs
@@ -25,14 +25,46 @@ fn solve1(size: u32, input: &str) -> u32 {
     ring[0] * ring[1]
 }
 
+fn solve2(input: &str) -> String {
+    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(|n| format!("{:02x}", n))
+        .collect()
+}
+
 fn main() {
     let mut input = String::new();
     io::stdin().read_to_string(&mut input).unwrap();
 
     println!("Part 1: {}", solve1(256, input.trim()));
+    println!("Part 2: {}", solve2(input.trim()));
 }
 
 #[test]
 fn part1() {
     assert_eq!(12, solve1(5, "3,4,1,5"));
 }
+
+#[test]
+fn part2() {
+    assert_eq!("a2582a3a0e66e6e86e3812dcb672a272", solve2(""));
+    assert_eq!("33efeb34ea91902bb2f59c9920caa6cd", solve2("AoC 2017"));
+    assert_eq!("3efbe78a8d82f29979031a4aa0b16a9d", solve2("1,2,3"));
+    assert_eq!("63960835bcdc130f0b66d7ff4f6a5a8e", solve2("1,2,4"));
+}