const std = @import("std");
const path = "../data/day11/input.txt";
const RetType = u11;
const grid_row = 10;
const grid_col = 10;
const GridType = u4;
const Grid = [grid_row][grid_col]GridType;
const Seen = [grid_row][grid_col]bool;
const directions = [8][2]i2{
    .{ -1, 0 },
    .{ 1, 0 },
    .{ 0, -1 },
    .{ 0, 1 },
    .{ -1, -1 },
    .{ 1, 1 },
    .{ 1, -1 },
    .{ -1, 1 },
};
fn parseInput() anyerror!Grid {
    const input = @embedFile(path);
    var lines = std.mem.tokenize(u8, input, "\n");
    var g: Grid = undefined;
    var row: usize = 0;
    while (lines.next()) |line| : (row += 1) {
        for (line) |_, col| {
            g[row][col] = try std.fmt.parseUnsigned(GridType, line[col .. col + 1], 10);
        }
    }
    return g;
}
pub fn first() anyerror!RetType {
    var grid = try parseInput();
    var flashes: RetType = 0;
    const max_step = 100;
    var step: u7 = 0;
    while (step < max_step) : (step += 1) {
        // increase each octupus energy by 1
        for (grid) |line, row| {
            for (line) |_, col| {
                grid[row][col] +|= 1;
            }
        }
        var seen = [_][grid_col]bool{[_]bool{false} ** grid_col} ** grid_row;
        // flash every octupus > 9
        for (grid) |line, row| {
            for (line) |energy, col| {
                if (energy > 9) {
                    flashes += flash(&seen, &grid, row, col);
                }
            }
        }
        // reset flashed
        for (grid) |line, row| {
            for (line) |energy, col| {
                if (energy > 9) {
                    grid[row][col] = 0;
                }
            }
        }
    }
    return flashes;
}
fn flash(seen: *Seen, grid: *Grid, row: usize, col: usize) RetType {
    var ret: RetType = 0;
    if ((seen[row][col]) or (grid[row][col] <= 9)) {
        return ret;
    }
    seen[row][col] = true;
    ret += 1;
    for (directions) |dir| {
        const diffrow = @intCast(i8, row) + dir[0];
        if ((diffrow < 0) or (diffrow >= grid_row)) continue;
        const diffcol = @intCast(i8, col) + dir[1];
        if ((diffcol < 0) or (diffcol >= grid_col)) continue;
        grid[@intCast(usize, diffrow)][@intCast(usize, diffcol)] +|= 1;
        ret += flash(seen, grid, @intCast(usize, diffrow), @intCast(usize, diffcol));
    }
    return ret;
}
pub fn main() anyerror!void {
    var timer = try std.time.Timer.start();
    const ret = try first();
    const t = timer.lap() / 1000;
    try std.testing.expectEqual(@as(RetType, 1700), ret);
    std.debug.print("Day 11a result: {d} \t\ttime: {d}µs\n", .{ ret, t });
}
test "day11a" {
    try std.testing.expectEqual(@as(RetType, 1700), try first());
}

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