48 lines
1.3 KiB
Rust
48 lines
1.3 KiB
Rust
/// Number of trailing zeros tells us which bit is set and there should only be one set
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/// Do some math to convert to the needed priority
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fn bits_to_priority(b: u64) -> u32 {
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let trailing = b.trailing_zeros();
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match trailing {
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0..=25 => trailing + 27,
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32..=57 => trailing - 31,
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_ => unreachable!(""),
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}
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}
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/// For each byte in the string offset it towards 0
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/// to make it fit in u64 and set a bit at the position of its value
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fn to_bits(s: &str) -> u64 {
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s.bytes().fold(0, |a, v| a | 1 << (v - 65))
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}
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pub fn part1(input: &str) -> impl std::fmt::Display {
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input
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.lines()
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.map(|l| l.split_at(l.len() / 2))
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.map(|(l, r)| bits_to_priority(to_bits(l) & to_bits(r)))
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.sum::<u32>()
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}
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pub fn part2(input: &str) -> impl std::fmt::Display {
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let mut lines = input.lines();
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let mut sum = 0;
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while let Some(l1) = lines.next() {
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let l2 = lines.next().expect("second is guaranteed to be there");
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let l3 = lines.next().expect("third is guaranteed to be there");
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sum += bits_to_priority(to_bits(l1) & to_bits(l2) & to_bits(l3));
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}
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sum
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}
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#[test]
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fn test_part1() {
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assert_eq!("15", part1("A Y\nB X\nC Z").to_string())
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}
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#[test]
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fn test_part2() {
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assert_eq!("12", part2("A Y\nB X\nC Z").to_string())
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}
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