2016/advent8.c

   1 #define _GNU_SOURCE 1
   2 #include <stdio.h>
   3 #include <string.h>
   4 #include <stdlib.h>
   5 #include <unistd.h>
   6 #include <stdbool.h>
   7 #include <ctype.h>
   8
   9 #define COLS 50
  10 #define ROWS 6
  11 bool grid[ROWS][COLS];
  12 bool row[COLS];
  13 bool col[ROWS];
  14
  15 int main(int argc, char **argv)
  16 {
  17   ssize_t nread;
  18   size_t len = 0;
  19   char *line = NULL;
  20   int count = 0;
  21   int i, j;
  22   while ((nread = getline(&line, &len, stdin)) >= 0) {
  23     char *end;
  24     int x, y;
  25     count++;
  26     if (!strncmp (line, "rect ", 5)) {
  27       x = strtol (line + 5, &end, 10);
  28       y = strtol (end + 1, NULL, 10);
  29       for (i = 0; i < y; i++)
  30         for (j = 0; j < x; j++)
  31           grid[i][j] = true;
  32     } else if (!strncmp (line, "rotate row y=", 13)) {
  33       x = strtol (line + 13, &end, 10);
  34       y = strtol (end + 3, NULL, 10);
  35       for (i = 0; i < COLS; i++)
  36         row[i] = grid[x][i];
  37       for (i = 0; i < COLS; i++)
  38         grid[x][(i + y) % COLS] = row[i];
  39     } else { // rotate column x=
  40       x = strtol (line + 16, &end, 10);
  41       y = strtol (end + 3, NULL, 10);
  42       for (i = 0; i < ROWS; i++)
  43         col[i] = grid[i][x];
  44       for (i = 0; i < ROWS; i++)
  45         grid[(i + y) % ROWS][x] = col[i];
  46     }
  47   }
  48   int lit = 0;
  49   for (i = 0; i < ROWS; i++) {
  50     for (j = 0; j < COLS; j++) {
  51       putchar (grid[i][j] ? '#' : ' ');
  52       if (grid[i][j])
  53         lit++;
  54     }
  55     putchar ('\n');
  56   }
  57   printf ("after %d instructions, %d pixels are lit\n", count, lit);
  58   return 0;
  59 }