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use std::collections::HashSet;
fn main() {
let input = advent::read_lines(8);
println!("8a: {}", count_unique_digits(&input));
println!("8b: {}", decode_digits(&input));
}
fn count_unique_digits<T: AsRef<str>>(input: &[T]) -> usize {
let mut sum = 0;
for line in input {
let segments = line.as_ref()
.split_once(" | ")
.map(|(_, s)| s)
.unwrap()
.split_terminator(' ')
.filter(|segment| [2,3,4,7].contains(&segment.len()))
.count();
sum += segments;
}
sum
}
#[derive(Default)]
struct SevenSegment {
top: Option<char>,
middle: Option<char>,
bottom: Option<char>,
topleft: Option<char>,
topright: Option<char>,
bottomleft: Option<char>,
bottomright: Option<char>,
}
fn deduce_decoder(signals: &[&str]) -> SevenSegment {
let mut decoder = SevenSegment::default();
let mut segment_counts : Vec<Vec<HashSet<char>>> = Vec::new();
for i in 0..10 {
let vec = signals.iter()
.filter(|s| s.len() == i)
.map(|&s| s.chars().collect())
.collect();
segment_counts.push(vec);
}
/* top element is difference between 7 and 1 */
decoder.top = Some(*segment_counts[3][0].difference(&segment_counts[2][0]).next().unwrap());
/* top right element is difference between 8 and 6 */
for s in &segment_counts[6] {
/* possible differences: 0, 6, 9 */
let diff = *segment_counts[7][0].difference(s).next().unwrap();
/* if the single different segment is also in 1, the checked segment is 6 */
if segment_counts[2][0].contains(&diff) {
decoder.topright = Some(diff);
}
}
/* with top and topright segments we can find bottomright segment via 7 */
let mut tmp = HashSet::new();
tmp.insert(decoder.top.unwrap());
tmp.insert(decoder.topright.unwrap());
decoder.bottomright = Some(*segment_counts[3][0].difference(&tmp).next().unwrap());
/* segments of 4 and 7 are contained in 9 */
for s in &segment_counts[6] {
if segment_counts[4][0].is_subset(s) {
let diff94 : HashSet<char> = s.difference(&segment_counts[4][0]).cloned().collect();
let diff947 = *diff94.difference(&segment_counts[3][0]).next().unwrap();
decoder.bottom = Some(diff947);
/* bottomleft is difference between 8 and 9 */
decoder.bottomleft = Some(*segment_counts[7][0].difference(s).next().unwrap());
}
}
/* 3 is the only 5-segment digit that fully contains 7 */
for s in &segment_counts[5] {
if segment_counts[3][0].is_subset(s) {
let mut tmp = segment_counts[3][0].clone();
tmp.insert(decoder.bottom.unwrap());
decoder.middle = Some(*s.difference(&tmp).next().unwrap());
}
}
/* topleft can be found with 4 and known decodings */
let mut tmp = HashSet::new();
tmp.insert(decoder.topright.unwrap());
tmp.insert(decoder.bottomright.unwrap());
tmp.insert(decoder.middle.unwrap());
decoder.topleft = Some(*segment_counts[4][0].difference(&tmp).next().unwrap());
decoder
}
fn possible_digits(decoder: &SevenSegment) -> Vec<HashSet<char>> {
let set0 = HashSet::from([
decoder.top.unwrap(), decoder.topright.unwrap(), decoder.bottomright.unwrap(),
decoder.bottom.unwrap(), decoder.bottomleft.unwrap(), decoder.topleft.unwrap(),
]);
let set1 = HashSet::from([
decoder.topright.unwrap(), decoder.bottomright.unwrap(),
]);
let set2 = HashSet::from([
decoder.top.unwrap(), decoder.topright.unwrap(), decoder.middle.unwrap(),
decoder.bottomleft.unwrap(), decoder.bottom.unwrap(),
]);
let set3 = HashSet::from([
decoder.top.unwrap(), decoder.topright.unwrap(), decoder.bottomright.unwrap(),
decoder.middle.unwrap(), decoder.bottom.unwrap(),
]);
let set4 = HashSet::from([
decoder.topleft.unwrap(), decoder.topright.unwrap(),
decoder.middle.unwrap(), decoder.bottomright.unwrap(),
]);
let set5 = HashSet::from([
decoder.top.unwrap(), decoder.topleft.unwrap(), decoder.middle.unwrap(),
decoder.bottomright.unwrap(), decoder.bottom.unwrap(),
]);
let set6 = HashSet::from([
decoder.top.unwrap(), decoder.topleft.unwrap(), decoder.middle.unwrap(),
decoder.bottomright.unwrap(), decoder.bottom.unwrap(), decoder.bottomleft.unwrap(),
]);
let set7 = HashSet::from([
decoder.top.unwrap(), decoder.topright.unwrap(), decoder.bottomright.unwrap(),
]);
let set8 = HashSet::from([
decoder.top.unwrap(), decoder.topleft.unwrap(), decoder.topright.unwrap(), decoder.middle.unwrap(),
decoder.bottomright.unwrap(), decoder.bottom.unwrap(), decoder.bottomleft.unwrap(),
]);
let set9 = HashSet::from([
decoder.top.unwrap(), decoder.topleft.unwrap(), decoder.topright.unwrap(), decoder.middle.unwrap(),
decoder.bottom.unwrap(), decoder.bottomright.unwrap(),
]);
Vec::from([set0, set1, set2, set3, set4, set5, set6, set7, set8, set9])
}
fn decode_digit(decoder: &SevenSegment, input: &str) -> usize {
let possible = possible_digits(decoder);
let segments : HashSet<char> = input.chars().collect();
possible.iter()
.enumerate()
.filter(|&(_, p)| segments == *p)
.map(|(i, _)| i)
.next()
.unwrap()
}
fn decode_digits<T: AsRef<str>>(input: &[T]) -> usize {
let mut number_sum = 0;
for line in input {
let (signals, segments) = line.as_ref()
.split_once(" | ")
.unwrap();
let signals : Vec<&str> = signals.split_terminator(' ').collect();
let segments : Vec<&str> = segments.split_terminator(' ').collect();
let decoder = deduce_decoder(&signals);
let mut number = 0;
for s in segments {
number *= 10;
number += decode_digit(&decoder, s);
}
number_sum += number;
}
number_sum
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test() {
let input = [
"be cfbegad cbdgef fgaecd cgeb fdcge agebfd fecdb fabcd edb | fdgacbe cefdb cefbgd gcbe",
"edbfga begcd cbg gc gcadebf fbgde acbgfd abcde gfcbed gfec | fcgedb cgb dgebacf gc",
"fgaebd cg bdaec gdafb agbcfd gdcbef bgcad gfac gcb cdgabef | cg cg fdcagb cbg",
"fbegcd cbd adcefb dageb afcb bc aefdc ecdab fgdeca fcdbega | efabcd cedba gadfec cb",
"aecbfdg fbg gf bafeg dbefa fcge gcbea fcaegb dgceab fcbdga | gecf egdcabf bgf bfgea",
"fgeab ca afcebg bdacfeg cfaedg gcfdb baec bfadeg bafgc acf | gebdcfa ecba ca fadegcb",
"dbcfg fgd bdegcaf fgec aegbdf ecdfab fbedc dacgb gdcebf gf | cefg dcbef fcge gbcadfe",
"bdfegc cbegaf gecbf dfcage bdacg ed bedf ced adcbefg gebcd | ed bcgafe cdgba cbgef",
"egadfb cdbfeg cegd fecab cgb gbdefca cg fgcdab egfdb bfceg | gbdfcae bgc cg cgb",
"gcafb gcf dcaebfg ecagb gf abcdeg gaef cafbge fdbac fegbdc | fgae cfgab fg bagce",
];
assert_eq!(count_unique_digits(&input), 26);
assert_eq!(decode_digits(&input), 61229);
}
}
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