aoc/year2016/
day06.rs

1//! # Signals and Noise
2//!
3//! The cardinality of uppercase letters is only 26 so we can use a fixed size array to
4//! count the frequency of each character efficiently.
5type Input = Vec<[u32; 26]>;
6
7pub fn parse(input: &str) -> Input {
8    let width = input.lines().next().unwrap().len();
9    let mut freq = vec![[0; 26]; width];
10
11    for (i, b) in input.bytes().filter(u8::is_ascii_lowercase).enumerate() {
12        freq[i % width][(b - b'a') as usize] += 1;
13    }
14
15    freq
16}
17
18pub fn part1(input: &Input) -> String {
19    find(input, |freq| {
20        freq.iter().enumerate().filter(|(_, f)| **f > 0).max_by_key(|(_, f)| **f).unwrap()
21    })
22}
23
24pub fn part2(input: &Input) -> String {
25    find(input, |freq| {
26        freq.iter().enumerate().filter(|(_, f)| **f > 0).min_by_key(|(_, f)| **f).unwrap()
27    })
28}
29
30fn find(input: &Input, ec: impl Fn(&[u32; 26]) -> (usize, &u32)) -> String {
31    input.iter().map(ec).map(|(index, _)| ((index as u8) + b'a') as char).collect()
32}
aoc/year2016/day06.rs

aoc/year2016/
day06.rs
