83e957d5f9
This doesn't actually matter for the input data given, but it ensures we get the right error when the battery list is too short, instead of unwrapping.
74 lines
1.9 KiB
Rust
74 lines
1.9 KiB
Rust
use crate::puzzle::Puzzle;
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use nom::{
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Parser,
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character::complete::{newline, satisfy},
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combinator::eof,
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error::Error,
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multi::{many1, separated_list1},
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sequence::terminated,
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};
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pub const PUZZLE: Puzzle<Vec<Vec<u8>>, 2> = Puzzle {
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number: 3,
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parser: |input| {
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terminated::<_, _, Error<&str>, _, _>(
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terminated(
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separated_list1(
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newline,
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many1(satisfy(|c| c.is_digit(10)).map(|c| c as u8 - '0' as u8)),
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),
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newline,
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),
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eof,
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)
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.parse(input)
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.unwrap()
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.1
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},
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parts: [
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|input| {
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input
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.iter()
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.map(|bank| {
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digits_to_int(&max_batteries(2, &bank).expect("battery list too short"))
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})
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.sum::<usize>()
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.to_string()
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},
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|input| {
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input
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.iter()
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.map(|bank| {
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digits_to_int(&max_batteries(12, &bank).expect("battery list too short"))
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})
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.sum::<usize>()
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.to_string()
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},
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],
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};
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fn max_batteries(n: usize, v: &[u8]) -> Option<Vec<u8>> {
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let mut result = Vec::with_capacity(n);
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let mut remaining = n;
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let mut slice = v;
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while remaining > 0 {
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if slice.len() - remaining + 1 == 0 {
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return None;
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}
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let (b, i) = find_max(&slice[..slice.len() - remaining + 1]);
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result.push(b);
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remaining -= 1;
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slice = &slice[i + 1..];
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}
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Some(result)
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}
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fn find_max<A: Ord + Copy>(v: &[A]) -> (A, usize) {
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let (n, x) = v.iter().enumerate().rev().max_by_key(|x| x.1).unwrap();
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(*x, n)
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}
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fn digits_to_int(digits: &[u8]) -> usize {
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digits.iter().fold(0, |acc, &d| acc * 10 + (d as usize))
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}
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