uint32_t pc_next_pos(dungeon_t *d, pair_t dir)
{
dir[dim_y] = dir[dim_x] = 0;
/* Tunnel to the nearest dungeon corner, then move around in hopes *
* of killing a couple of monsters before we die ourself. */
if (in_corner(d, &d->pc)) {
/*
dir[dim_x] = (mapxy(d->pc.position[dim_x] - 1,
d->pc.position[dim_y]) ==
ter_wall_immutable) ? 1 : -1;
*/
dir[dim_y] = (mapxy(d->pc.position[dim_x],
d->pc.position[dim_y] - 1) ==
ter_wall_immutable) ? 1 : -1;
} else {
dir_nearest_wall(d, &d->pc, dir);
}
return 0;
}
int main() {
const int line_length = 100;
int lights[2][line_length + 2][line_length + 2];
for (int j = 0; j < line_length + 2; ++j) {
for (int i = 0; i < line_length + 2; ++i) {
if (in_corner(i, j, line_length)) {
lights[0][j][i] = lights[1][j][i] = 1;
}
else {
lights[0][j][i] = lights[1][j][i] = 0;
}
}
}
char line[BUFFER];
FILE *input = fopen("day18.txt", "r");
int line_number = 1;
while (fgets(line, BUFFER, input)) {
for (int c = 0; c < line_length; ++c) {
if (line[c] == '#') {
lights[0][line_number][c+1] = 1;
}
else if (line[c] == '.') {
lights[0][line_number][c+1] = 0;
}
else {
printf("unrecognised character: %c\n", line[c]);
}
}
++line_number;
}
int old_index = 0;
int new_index = 1;
for (int t = 0; t < 100; ++t) {
for (int j = 1; j <= line_length; ++j) {
for (int i = 1; i <= line_length; ++i) {
if (in_corner(i, j, line_length)) continue;
int neighbours_on = 0;
for (int y = j - 1; y <= j + 1; ++y) {
for (int x = i - 1; x <= i + 1; ++x) {
if (y == j && x == i) continue;
if (lights[old_index][y][x]) ++neighbours_on;
}
}
if (lights[old_index][j][i] && neighbours_on < 2 || neighbours_on > 3) {
lights[new_index][j][i] = 0;
}
else if (neighbours_on == 3) {
lights[new_index][j][i] = 1;
}
else {
lights[new_index][j][i] = lights[old_index][j][i];
}
}
}
old_index = (old_index + 1) % 2;
new_index = (new_index + 1) % 2;
}
int lights_on = 0;
for (int j = 1; j <= line_length; ++j) {
for (int i = 1; i <= line_length; ++i) {
if (lights[old_index][j][i]) ++lights_on;
}
}
printf("%d\n", lights_on);
return 0;
}
