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day06.rs
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day06.rs
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//! # Custom Customs
//!
//! This is a disguised binary question like the previous [`day 5`].
//!
//! We can store each passenger's answers as an implicit set in a `u32` since the cardinality
//! is only 26. For each yes answer we set a bit, shifting left based on the letter. For example
//! `acf` would be represented as `100101`.
//!
//! For part one to find groups where any person answered yes, we reduce the group using
//! [bitwise OR](https://en.wikipedia.org/wiki/Bitwise_operation) then count the number of ones
//! for each group using the blazing fast [`count_ones`] intrinsic.
//!
//! Part two is very similar, except that we use a bitwise AND instead.
//!
//! [`day 5`]: crate::year2020::day05
//! [`count_ones`]: u32::count_ones
pub fn parse(input: &str) -> Vec<u32> {
input.lines().map(|line| line.bytes().fold(0, |acc, b| acc | 1 << (b - b'a'))).collect()
}
pub fn part1(input: &[u32]) -> u32 {
let mut total = 0;
let mut group = u32::MIN;
for &passenger in input {
if passenger == 0 {
total += group.count_ones();
group = u32::MIN;
} else {
group |= passenger;
}
}
total + group.count_ones()
}
pub fn part2(input: &[u32]) -> u32 {
let mut total = 0;
let mut group = u32::MAX;
for &passenger in input {
if passenger == 0 {
total += group.count_ones();
group = u32::MAX;
} else {
group &= passenger;
}
}
total + group.count_ones()
}