115 lines
2.7 KiB
Rust
115 lines
2.7 KiB
Rust
use std::fs;
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type SeatCode = [char; 10];
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fn main() -> Result<(), Box<dyn std::error::Error>> {
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let input = fs::read_to_string("input")?;
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// Part 1
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let max_id: Result<usize, String> = input
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.lines()
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.map(|code| {
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let (row, col) = find_seat(parse_seatcode(code)?);
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Ok(row * 8 + col)
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})
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.max()
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.ok_or("No seat codes set")?;
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println!("{}", max_id?);
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// Part 2
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let mut ids = input
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.lines()
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.map(|code| {
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let (row, col) = find_seat(parse_seatcode(code)?);
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Ok(row * 8 + col)
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})
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.collect::<Result<Vec<usize>, String>>()?;
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ids.sort();
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let mut previous = ids[0];
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for id in &ids[1..] {
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if id - 1 != previous {
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println!("{}", id);
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break;
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} else {
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previous = *id;
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}
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}
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Ok(())
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}
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fn parse_seatcode(input: &str) -> Result<SeatCode, String> {
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let mut output = ['0'; 10];
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for (i, c) in input.chars().enumerate() {
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if i > 10 {
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Err(format!("Seat code too long: '{}'", input))?;
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}
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if !['F', 'B', 'L', 'R'].iter().any(|valid| &c != valid) {
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Err(format!("Invalid character in seat code: '{}'", input))?;
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}
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output[i] = c;
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}
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Ok(output)
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}
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fn find_seat(code: SeatCode) -> (usize, usize) {
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let midpoint = |(start, end): (usize, usize)| (start + end) / 2;
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let binary_follow = |range: (usize, usize), direction: &char| match direction {
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'F' | 'L' => (range.0, midpoint(range)),
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'B' | 'R' => (midpoint(range) + 1, range.1),
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_ => unreachable!("We already checked all characters are valid"),
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};
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let row = code[..7].iter().fold((0, 127), binary_follow).0;
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let col = code[7..].iter().fold((0, 7), binary_follow).0;
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(row, col)
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn test_simple() -> Result<(), Box<dyn std::error::Error>> {
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let input = "FBFBBFFRLR";
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let seat = find_seat(parse_seatcode(input)?);
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assert_eq!(seat, (44, 5));
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Ok(())
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}
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#[test]
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fn test_simple2() -> Result<(), Box<dyn std::error::Error>> {
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let input = "BFFFBBFRRR";
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let seat = find_seat(parse_seatcode(input)?);
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assert_eq!(seat, (70, 7));
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Ok(())
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}
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#[test]
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fn test_simple3() -> Result<(), Box<dyn std::error::Error>> {
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let input = "FFFBBBFRRR";
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let seat = find_seat(parse_seatcode(input)?);
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assert_eq!(seat, (14, 7));
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Ok(())
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}
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#[test]
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fn test_simple4() -> Result<(), Box<dyn std::error::Error>> {
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let input = "BBFFBBFRLL";
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let seat = find_seat(parse_seatcode(input)?);
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assert_eq!(seat, (102, 4));
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Ok(())
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}
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}
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