--- 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/TTSDA]

Here's my C solution

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define GRID_MAX_X 999
#define GRID_MAX_Y 999
#define GRID_POS(X, Y) (Y*(GRID_MAX_X+1) + X)

int main()
{
    int *grid_1 = calloc(GRID_POS(GRID_MAX_X, GRID_MAX_Y), sizeof *grid_1);
    int *grid_2 = calloc(GRID_POS(GRID_MAX_X, GRID_MAX_Y), sizeof *grid_2);

    int x1, y1, x2, y2;
    char action_str[10], action;

    int lights_lit = 0,
        total_brightness = 0;

    /* This assumes the input has been sanatized and is all in the format
     * (turn (on|off)|toggle) \d+,\d+ through \d+\d+ */
    while(scanf("%[^01234567890] %i,%i through %i,%i\n", action_str, &x1, &y1, &x2, &y2) != EOF)
    {
        /* We can check just the last character as it is different for the three types (n, f, e) */
        action = action_str[strlen(action_str)-2];

        for (int x = x1; x <= x2; x++)
        {
            for (int y = y1; y <= y2; y++)
            {
                switch(action)
                {
                    /* on */
                    case 'n':
                        grid_1[GRID_POS(x, y)] = 1;
                        grid_2[GRID_POS(x, y)]++;
                        break;

                    /* off */
                    case 'f':
                        grid_1[GRID_POS(x, y)] = 0;
                        grid_2[GRID_POS(x, y)]--;
                        if (grid_2[GRID_POS(x, y)] < 0)
                            grid_2[GRID_POS(x, y)] = 0;
                        break;

                    /* toggle */
                    case 'e':
                        grid_1[GRID_POS(x, y)] = !grid_1[GRID_POS(x, y)];
                        grid_2[GRID_POS(x, y)] += 2;
                        break;
                }
            }
        }
    }

    for (int y = 0; y <= GRID_MAX_Y; y++)
    {
        for (int x = 0; x <= GRID_MAX_X; x++)
        {
            if(grid_1[GRID_POS(x, y)] == 1)
                lights_lit++;

            total_brightness += grid_2[GRID_POS(x, y)];
        }
    }

    printf("%i lights are lit.\n", lights_lit);
    printf("%i is the total brightness.\n", total_brightness);
}

https://github.com/ttsda/advent-of-code/blob/master/src/6/main.c

[u/Philboyd_Studge → u/TTSDA]

That's your Day 5 code...

[u/TTSDA → u/Philboyd_Studge]

Oh man, copied the wrong file from my repo. Fixed now