2017/advent10.c

   1 #define _GNU_SOURCE 1
   2 #include <stdio.h>
   3 #include <string.h>
   4 #include <stdlib.h>
   5 #include <unistd.h>
   6
   7 #if 0 // part 1
   8
   9 int main(int argc, char **argv)
  10 {
  11   if (argc != 3)
  12     return 1;
  13   int size = atoi(argv[1]);
  14   if (size < 2 || size > 256)
  15     return 2;
  16   unsigned char *list = malloc (size);
  17   for (int i = 0; i < size; i++)
  18     list[i] = i;
  19   char *p = argv[2];
  20   char *end;
  21   int skip = 0;
  22   int pos = 0;
  23   int length;
  24   while ((length = strtol (p, &end, 10)), p != end) {
  25     printf ("length %d, skip %d, pos %d\n", length, skip, pos % size);
  26     for (int i = 0; i < length / 2; i++) {
  27       int tmp = list[(i + pos) % size];
  28       list[(i + pos) % size] = list[(length - i - 1 + pos) % size];
  29       list[(length - i - 1 + pos) % size] = tmp;
  30     }
  31     if (size == 5)
  32       printf (" %d %d %d %d %d\n", list[0], list[1], list[2], list[3], list[4]);
  33     pos += length + skip++;
  34     p = end + 1;
  35   }
  36   printf ("final product %d\n", list[0] * list[1]);
  37   return 0;
  38 }
  39
  40 #else // part 2
  41
  42 int main(int argc, char **argv)
  43 {
  44   if (argc != 2)
  45     return 1;
  46   const int size = 256;
  47   unsigned char list[size];
  48   for (int i = 0; i < size; i++)
  49     list[i] = i;
  50   int skip = 0;
  51   int pos = 0;
  52   const char suffix[6] = { 17, 31, 73, 47, 23 };
  53   char *str = malloc(strlen(argv[1]) + 5 + 1);
  54   strcpy(stpcpy(str, argv[1]), suffix);
  55   for (int j = 0; j < 64; j++) {
  56     printf ("round %d, skip %d, pos %d\n", j, skip, pos % size);
  57     for (char *p = str; *p; p++) {
  58       int length = *p;
  59       for (int i = 0; i < length / 2; i++) {
  60         int tmp = list[(i + pos) % size];
  61         list[(i + pos) % size] = list[(length - i - 1 + pos) % size];
  62         list[(length - i - 1 + pos) % size] = tmp;
  63       }
  64       pos += length + skip++;
  65     }
  66   }
  67   unsigned char chunk = 0;
  68   for (int i = 0; i < size; i++) {
  69     chunk ^= list[i];
  70     if (i % 16 == 15) {
  71       printf ("%02x", chunk);
  72       chunk = 0;
  73     }
  74   }
  75   puts ("");
  76   return 0;
  77 }
  78
  79 #endif