75 lines
1.9 KiB
Rust
75 lines
1.9 KiB
Rust
//! Day 08 of 2021.
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mod display;
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use display::{CharSet, Display};
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use crate::prelude::*;
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/// Get the solution for day 08 of 2021.
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pub fn solution() -> Solution {
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Solution::new(Day::new(8, 2021), part_1, part_2).with_expected(521, 1016804)
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}
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/// The logic to solve part one.
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fn part_1(input: &str) -> Result<String> {
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Ok(
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input
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.lines()
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.map(|line| {
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line
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.split(" | ")
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.nth(1)
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.ok_or_else(|| eyre!("Invalid input: {}", line))
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})
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.collect::<Result<Vec<_>>>()?
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.into_iter()
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.flat_map(|line| line.split(' ').map(Display::parse))
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.filter(|display| [2, 4, 3, 7].contains(&display.0))
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.count()
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.to_string(),
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)
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}
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/// The logic to solve part two.
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fn part_2(input: &str) -> Result<String> {
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let mut sum = 0;
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for line in input.lines() {
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let mut split = line.split(" | ");
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// Figure out the displays from the signal side.
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let displays = Display::figure_out_from_others(
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split
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.next()
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.ok_or_else(|| eyre!("Invalid input: {}", line))?
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.split(' ')
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.map(Display::parse)
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.collect::<Vec<_>>(),
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)?;
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// Get all the CharSets from the encoded side.
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let encoded = split
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.next()
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.ok_or_else(|| eyre!("Invalid input: {}", line))?
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.split(' ')
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.map(str::chars)
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.map(CharSet::from_iter);
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// Loop through the encoded numbers backwards so we can use the loop index
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// to multiply it by 10 to the power of the index.
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// So 123 would be (3 * 1) + (2 * 10) + (1 * 100).
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for (index, set) in encoded.rev().enumerate() {
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let decoded_number = displays
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.iter()
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.find(|display| display.1 == &set)
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.map(|display| display.0)
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.ok_or_else(|| eyre!("Impossible to decode {:?}", set))?;
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sum += 10_isize.pow(index as u32) * decoded_number;
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}
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}
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Ok(sum.to_string())
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}
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