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πŸͺ - 2023 DAY 14 SOLUTIONS -πŸͺ

Day 14: Parabolic Reflector Dish

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  • The first part was simple enough. Adding in the 3 remaining tilt methods for star 2 was also simple enough, and worked just how I figured it would. Tried the brute force solution first, but realized it was going to take a ridiculous amount of time and went back to figure out an algorithm. It was simple enough to guess that it would hit a point where it just repeats infinitely, but actually coding out the math to extrapolate that took way more time than I want to admit. Not sure why I struggled with it so much, but after some pen and paper mathing, I essentially got there. Ended up having to subract 1 from this calculation, and either I'm just missing something or am way too tired, because I don't know why it's one less than what I thought it would be, but it works so who am I to complain.

    https://github.com/capitalpb/advent_of_code_2023/blob/main/src/solvers/day14.rs

    use crate::Solver;
    
    #[derive(Debug)]
    struct PlatformMap {
        tiles: Vec>,
    }
    
    impl PlatformMap {
        fn from(input: &str) -> PlatformMap {
            PlatformMap {
                tiles: input.lines().map(|line| line.chars().collect()).collect(),
            }
        }
    
        fn load(&self) -> usize {
            self.tiles
                .iter()
                .enumerate()
                .map(|(row, tiles)| {
                    tiles.iter().filter(|tile| *tile == &'O').count() * (self.tiles.len() - row)
                })
                .sum()
        }
    
        fn tilt_north(&mut self) {
            for row in 1..self.tiles.len() {
                for col in 0..self.tiles[0].len() {
                    if self.tiles[row][col] != 'O' {
                        continue;
                    }
    
                    let mut new_row = row;
                    for check_row in (0..row).rev() {
                        if self.tiles[check_row][col] == '.' {
                            new_row = check_row;
                        } else {
                            break;
                        }
                    }
    
                    self.tiles[row][col] = '.';
                    self.tiles[new_row][col] = 'O';
                }
            }
        }
    
        fn tilt_west(&mut self) {
            for col in 1..self.tiles[0].len() {
                for row in 0..self.tiles.len() {
                    if self.tiles[row][col] != 'O' {
                        continue;
                    }
    
                    let mut new_col = col;
                    for check_col in (0..col).rev() {
                        if self.tiles[row][check_col] == '.' {
                            new_col = check_col;
                        } else {
                            break;
                        }
                    }
    
                    self.tiles[row][col] = '.';
                    self.tiles[row][new_col] = 'O';
                }
            }
        }
    
        fn tilt_south(&mut self) {
            for row in (0..(self.tiles.len() - 1)).rev() {
                for col in 0..self.tiles[0].len() {
                    if self.tiles[row][col] != 'O' {
                        continue;
                    }
    
                    let mut new_row = row;
                    for check_row in (row + 1)..self.tiles.len() {
                        if self.tiles[check_row][col] == '.' {
                            new_row = check_row;
                        } else {
                            break;
                        }
                    }
    
                    self.tiles[row][col] = '.';
                    self.tiles[new_row][col] = 'O';
                }
            }
        }
    
        fn tilt_east(&mut self) {
            for col in (0..(self.tiles[0].len() - 1)).rev() {
                for row in 0..self.tiles.len() {
                    if self.tiles[row][col] != 'O' {
                        continue;
                    }
    
                    let mut new_col = col;
                    for check_col in (col + 1)..self.tiles[0].len() {
                        if self.tiles[row][check_col] == '.' {
                            new_col = check_col;
                        } else {
                            break;
                        }
                    }
    
                    self.tiles[row][col] = '.';
                    self.tiles[row][new_col] = 'O';
                }
            }
        }
    }
    
    pub struct Day14;
    
    impl Solver for Day14 {
        fn star_one(&self, input: &str) -> String {
            let mut platform_map = PlatformMap::from(input);
            platform_map.tilt_north();
            platform_map.load().to_string()
        }
    
        fn star_two(&self, input: &str) -> String {
            let mut platform_map = PlatformMap::from(input);
            let mut map_history: Vec>> = vec![];
    
            for index in 0..1_000_000_000 {
                platform_map.tilt_north();
                platform_map.tilt_west();
                platform_map.tilt_south();
                platform_map.tilt_east();
    
                if let Some(repeat_start) = map_history
                    .iter()
                    .position(|tiles| tiles == &platform_map.tiles)
                {
                    let repeat_length = index - repeat_start;
                    let delta = (1_000_000_000 - repeat_start) % repeat_length;
                    let solution_index = repeat_start + delta - 1;
    
                    return PlatformMap {
                        tiles: map_history[solution_index].clone(),
                    }
                    .load()
                    .to_string();
                }
    
                map_history.push(platform_map.tiles.clone());
            }
    
            platform_map.load().to_string()
        }
    }
    
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