Advent of Code 2023 Day 14 Part 2

main.rs

struct Grid {
    width: usize,
    height: usize,
    data: Vec<u8>
}

fn get_grid() -> Grid {
    let mut grid = Grid {
        width: 0,
        height: 0,
        data: std::fs::read("input").unwrap()
    };

    grid.width = grid.data.iter().position(|c| *c == b'\n').unwrap();
    grid.data.retain(|c| *c != b'\n');
    grid.height = grid.data.len() / grid.width;
    assert!(grid.data.len() % grid.width == 0);
    return grid;
}

fn rotate_north(grid: &mut Grid) {
    for y in 1..grid.height {
        for x in 0..grid.width {
            let index = y * grid.width + x;
            if grid.data[index] == b'O' {
                let mut move_to = index;
                for col in (0..y).rev() {
                    let test = col * grid.width + x;
                    if grid.data[test] != b'.' {
                        break;
                    }
                    move_to = test;
                }
                grid.data.swap(index, move_to);
            }
        }
    }
}

fn rotate_south(grid: &mut Grid) {
    for y in (0..grid.height - 1).rev() {
        for x in 0..grid.width {
            let index = y * grid.width + x;
            if grid.data[index] == b'O' {
                let mut move_to = index;
                for col in y + 1..grid.height {
                    let test = col * grid.width + x;
                    if grid.data[test] != b'.' {
                        break;
                    }
                    move_to = test;
                }
                grid.data.swap(index, move_to);
            }
        }
    }
}

fn rotate_west(grid: &mut Grid) {
    for x in 1..grid.width {
        for y in 0..grid.height {
            let index = y * grid.width + x;
            if grid.data[index] == b'O' {
                let mut move_to = index;
                for row in (0..x).rev() {
                    let test = y * grid.width + row;
                    if grid.data[test] != b'.' {
                        break;
                    }
                    move_to = test;
                }
                grid.data.swap(index, move_to);
            }
        }
    }
}

fn rotate_east(grid: &mut Grid) {
    for x in (0..grid.width - 1).rev() {
        for y in 0..grid.height {
            let index = y * grid.width + x;
            if grid.data[index] == b'O' {
                let mut move_to = index;
                for row in x + 1..grid.width {
                    let test = y * grid.width + row;
                    if grid.data[test] != b'.' {
                        break;
                    }
                    move_to = test;
                }
                grid.data.swap(index, move_to);
            }
        }
    }
}

fn main() {
    let mut grid = get_grid();
    for i in 0..1000000000 {
        rotate_north(&mut grid);
        rotate_west(&mut grid);
        rotate_south(&mut grid);
        rotate_east(&mut grid);
        if i % 100000 == 0 {
            let percentage = i as f64 / 10000000.0;
            println!("{percentage}%");
        }
    }
    let mut answer = 0;
    let mut mul = grid.height;
    for y in 0..grid.height {
        let mut num_rocks = 0;
        for x in 0..grid.width {
            if grid.data[y * grid.width + x] == b'O' {
                num_rocks += 1;
            }
        }
        answer += num_rocks * mul;
        mul -= 1;
    }
    println!("\nAnswer: {answer}");
}