From 83336085cc3f1c9900ab24e164643d32b7c38c01 Mon Sep 17 00:00:00 2001 From: June McEnroe Date: Wed, 21 Dec 2016 23:33:00 -0500 Subject: Day 21 part 2 --- src/bin/day21.rs | 30 +++++++++++++++++++++++++++--- 1 file changed, 27 insertions(+), 3 deletions(-) diff --git a/src/bin/day21.rs b/src/bin/day21.rs index c9abb76..982bf8a 100644 --- a/src/bin/day21.rs +++ b/src/bin/day21.rs @@ -87,7 +87,7 @@ impl<'a> From<&'a str> for Operation { } } -fn solve(password: &str, input: &str) -> String { +fn solve1(password: &str, input: &str) -> String { let mut password = password.as_bytes().to_owned(); for operation in input.lines().map(Operation::from) { @@ -97,11 +97,35 @@ fn solve(password: &str, input: &str) -> String { String::from_utf8(password).unwrap() } +fn solve2(scrambled: &str, input: &str) -> String { + let operations: Vec<_> = input.lines().map(Operation::from).collect(); + + let mut password = "abcdefgh".as_bytes().to_owned(); + let len = password.len(); + + loop { + let k = (0..(len - 1)).rev().find(|&k| password[k] < password [k + 1]).unwrap(); + let l = ((k + 1)..len).rev().find(|&l| password[k] < password[l]).unwrap(); + password.swap(k, l); + password[(k + 1)..].reverse(); + + let mut candidate = password.clone(); + for operation in &operations { + operation.apply(&mut candidate); + } + + if candidate == scrambled.as_bytes() { + return String::from_utf8(password).unwrap(); + } + } +} + fn main() { let mut input = String::new(); io::stdin().read_to_string(&mut input).unwrap(); - println!("Part 1: {}", solve("abcdefgh", &input)); + println!("Part 1: {}", solve1("abcdefgh", &input)); + println!("Part 2: {}", solve2("fbgdceah", &input)); } #[test] @@ -116,5 +140,5 @@ move position 3 to position 0 rotate based on position of letter b rotate based on position of letter d "; - assert_eq!("decab", solve("abcde", input.trim())); + assert_eq!("decab", solve1("abcde", input.trim())); } -- cgit 1.4.1