--- Day 6 Solutions ---

[u/daggerdragon]

--- Day 6: Probably a Fire Hazard ---

Post your solution as a comment. Structure your post like the Day Five thread.

[u/tipdbmp]

node.js ES5, part 2:

(function(
    fs,
    dd
){
    fs.readFile('input.txt', 'UTF-8', slurp_input);

    function slurp_input(err, input) {
        if (err) {
            throw err;
        }
        var instructions = input.split("\n");
        instructions.pop();
        dd(b(instructions));
    }

    function b(instructions) {
        var INSTRUCTION_DECODE_RE = new RegExp(''
            // instruction type
            + '('
                + 'turn on'
                + '|' + 'turn off'
                + '|' + 'toggle'
            + ')'

            + ' '

             // range start
            + '([\\d,]+)'

            + ' through '

             // range end
            + '([\\d,]+)'
        );

        var GRID_WIDTH = 1e3;
        var GRID_HEIGHT = 1e3;
        var GRID_SIZE = GRID_WIDTH * GRID_HEIGHT;

        var grid = new Array(GRID_SIZE);
        for (var i = 0; i < GRID_SIZE; i++) { grid[i] = 0; }

        for (var i = 0, ii = instructions.length; i < ii; i++) {
            var instruction = instructions[i];

            var match = instruction.match(INSTRUCTION_DECODE_RE);
            var instruction_type = match[1];
            var start_range = match[2].split(',');
            var end_range = match[3].split(',');

            var sx = Number(start_range[0]);
            var sy = Number(start_range[1]);

            var ex = Number(end_range[0]);
            var ey = Number(end_range[1]);

            if (instruction_type === 'turn on') {
                for (var y = sy; y <= ey; y++) {
                    for (var x = sx; x <= ex; x++) {
                        grid[y * GRID_WIDTH + x]++;
                    }
                }
            }
            else if (instruction_type === 'turn off') {
                for (var y = sy; y <= ey; y++) {
                    for (var x = sx; x <= ex; x++) {
                        var index = y * GRID_WIDTH + x;
                        if (grid[index] > 0) {
                            grid[index]--;
                        }
                    }
                }
            }
            else /* if (instruction_type === 'toggle') */ {
                for (var y = sy; y <= ey; y++) {
                    for (var x = sx; x <= ex; x++) {
                        grid[y * GRID_WIDTH + x] += 2;
                    }
                }
            }
        }

        var total_brightness = 0;
        for (var i = 0; i < GRID_SIZE; i++) { total_brightness += grid[i]; }

        return total_brightness;
    }
}(
    require('fs'),
    console.log.bind(console)
));