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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 solve1(size: u32, input: &str) -> u32 {
let mut ring: Vec<_> = (0..size).collect();
let mut index = 0;
let mut skip = 0;
for len in input.split(',').map(str::parse).map(Result::unwrap) {
reverse(&mut ring, index, len);
index += len + skip;
index %= ring.len();
skip += 1;
}
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"));
}
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