Created
December 8, 2021 10:08
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fn str_split_once<'a>(s: &'a str, pat: &str) -> Option<(&'a str, &'a str)> { | |
match s.split(pat).collect::<Vec<_>>()[..] { | |
[x, y] => Some((x, y)), | |
_ => None | |
} | |
} | |
fn day8(part: char, s: &str) -> String{ | |
if part == 'a' { | |
s.lines().flat_map(|line| { | |
let (_, o) = str_split_once(line, " | ").unwrap(); | |
o.split(" ").filter(|word| matches!(word.len(), 2 | 3 | 4 | 7)) | |
}).count().to_string() | |
} else { | |
s.lines().map(|line| { | |
// we only need to identify enough segments to distinguish 2/3/5 an 0/6/9. | |
// For 2/3 we need E or F. For 3/5 we need B or C. | |
// Further we need two of C for 6, D for 0 or E for 9. | |
// C (top right) and E (bottom left) will suffice. | |
// C appears in 1 and in 8 digits total. E appears in 4 digits total. | |
let (i, o) = str_split_once(line, " | ").unwrap(); | |
let dig_1 = i.split(" ").find(|word| word.len() == 2).unwrap(); | |
let seg_c = ('a' ..= 'g').find(|&sc| | |
dig_1.contains(sc) && i.chars().filter(|&ic| ic == sc).count() == 8 | |
).unwrap(); | |
let seg_e = ('a' ..= 'g').find(|&sc| | |
i.chars().filter(|&ic| ic == sc).count() == 4 | |
).unwrap(); | |
o.split(" ").map(|word| match (word.len(), word.contains(seg_c), word.contains(seg_e)) { | |
(2, true, false) => 1, (3, true, false) => 7, (4, true, false) => 4, | |
(5, true, true) => 2, (5, true, false) => 3, (5, false, false) => 5, | |
(6, true, true) => 0, (6, false, true) => 6, (6, true, false) => 9, | |
(7, true, true) => 8, _ => panic!("{} | {}", i, word) | |
}).reduce(|a, d| 10 * a + d).unwrap() | |
}).sum::<usize>().to_string() | |
} | |
} |
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