92 lines
2.2 KiB
Rust
92 lines
2.2 KiB
Rust
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use std::fs;
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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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let slope = parse_slope(&input)?;
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// Part 1
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let encounters = count_encounters(&slope, (1, 3));
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println!("{}", encounters);
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// Part 2
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let encounters: usize = [(1, 1), (1, 3), (1, 5), (1, 7), (2, 1)]
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.iter()
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.map(|angle| count_encounters(&slope, *angle))
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.product();
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println!("{}", encounters);
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Ok(())
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}
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fn parse_slope(input: &str) -> Result<Vec<Vec<usize>>, String> {
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input
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.lines()
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.map(|line| {
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line.chars()
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.map(|c| match c {
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'.' => Ok(0),
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'#' => Ok(1),
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other => Err(format!("Invalid slope; contains character: {}", other)),
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})
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.collect()
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})
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.collect()
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}
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fn count_encounters(input: &Vec<Vec<usize>>, angle: (usize, usize)) -> usize {
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input
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.iter()
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.enumerate()
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.step_by(angle.0)
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.map(|(i, row)| row[(i * angle.1 / angle.0) % row.len()])
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.sum()
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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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use indoc::indoc;
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#[test]
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fn test_simple() -> Result<(), Box<dyn std::error::Error>> {
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let example = indoc!(
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"..##.......
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#...#...#..
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.#....#..#.
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..#.#...#.#
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.#...##..#.
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..#.##.....
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.#.#.#....#
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.#........#
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#.##...#...
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#...##....#
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.#..#...#.#"
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);
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let parsed = parse_slope(example)?;
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assert_eq!(count_encounters(&parsed, (1, 3)), 7);
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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 example = indoc!(
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"..##.......
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#...#...#..
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.#....#..#.
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..#.#...#.#
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.#...##..#.
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..#.##.....
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.#.#.#....#
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.#........#
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#.##...#...
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#...##....#
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.#..#...#.#"
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);
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let parsed = parse_slope(example)?;
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assert_eq!(count_encounters(&parsed, (2, 1)), 2);
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Ok(())
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}
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}
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