2016/advent21.c

   1 #define _GNU_SOURCE 1
   2 #include <stdio.h>
   3 #include <string.h>
   4 #include <stdlib.h>
   5 #include <unistd.h>
   6 #include <assert.h>
   7
   8 #define MAX 100 // cheat by using wc on input file
   9 char buf[30 * MAX];
  10 char *lines[MAX];
  11
  12 int main(int argc, char **argv)
  13 {
  14   char array[9] = "fbgdceah";
  15   char tmp[9];
  16   int limit = strlen (array);
  17   if (argc > 1)
  18     limit = atoi (argv[1]);
  19   if (argc > 2)
  20     freopen (argv[2], "r", stdin);
  21   array[limit] = '\0';
  22   int nread = fread (buf, 1, sizeof buf, stdin);
  23   char *p = buf;
  24   int count = 0;
  25   do {
  26     lines[count++] = p;
  27     p = strchr (p, '\n');
  28     *p++ = '\0';
  29   } while (p - buf < nread);
  30   printf ("parsed %d lines, now reversing them\n", count);
  31   int a, b;
  32   char c, x, y;
  33   for (int i = count; i--; ) {
  34     printf ("iteration %d %s: ", i, lines[i]);
  35     if (!strncmp (lines[i], "swap", 4)) {
  36       a = sscanf (lines[i], "swap %c%*s %c with %*s %c", &c, &x, &y);
  37       assert (a == 3);
  38       if (c == 'p') {
  39         c = array[x - '0'];
  40         array[x - '0'] = array[y - '0'];
  41         array[y - '0'] = c;
  42       } else {
  43         assert (c == 'l');
  44         for (a = 0; a < limit; a++)
  45           if (array[a] == x)
  46             array[a] = y;
  47           else if (array[a] == y)
  48             array[a] = x;
  49       }
  50     } else if (!strncmp (lines[i], "rotate", 6)) {
  51       a = sscanf (lines[i], "rotate %c", &c);
  52       assert (a == 1);
  53       if (c == 'b') {
  54         a = sscanf (&lines[i][7], "%*s on position of letter %c", &c);
  55         assert (a == 1);
  56         b = strchr (array, c) - array;
  57         assert (b < limit);
  58         b = (b & 1) ? limit - (b + 1) / 2 : b ? 3 - b / 2 : 7;
  59       } else {
  60         a = sscanf (&lines[i][7], "%*s %d s%*s", &b);
  61         assert (a == 1);
  62         if (c == 'r')
  63           b = limit - b;
  64       }
  65       for (a = 0; a < limit; a++)
  66         tmp[(a + b) % limit] = array[a];
  67       memcpy (array, tmp, limit);
  68     } else if (!strncmp (lines[i], "reverse", 7)) {
  69       c = sscanf (lines[i], "reverse positions %d through %d", &a, &b);
  70       assert (c == 2);
  71       for (c = 0; c < (b - a + 1) / 2; c++) {
  72         x = array[c + a];
  73         array[c + a] = array[b - c];
  74         array[b - c] = x;
  75       }
  76     } else {
  77       assert (!strncmp (lines[i], "move", 4));
  78       c = sscanf (lines[i], "move position %d to position %d", &b, &a);
  79       assert (c == 2);
  80       x = array[a];
  81       if (a < b)
  82         memmove (array + a, array + a + 1, b - a);
  83       else
  84         memmove (array + b + 1, array + b, a - b);
  85       array[b] = x;
  86     }
  87     printf ("%s\n", array);
  88   }
  89   printf ("original string: %s\n", array);
  90   return 0;
  91 }