2017/advent8.c

   1 #define _GNU_SOURCE 1
   2 #include <stdio.h>
   3 #include <string.h>
   4 #include <stdlib.h>
   5 #include <unistd.h>
   6
   7 // cheat - pre-examined input to learn max name length (3+NUL)
   8 #define MAXNAME 4
   9
  10 typedef struct reg reg;
  11 struct reg {
  12   char name[MAXNAME];
  13   int value;
  14   reg *next;
  15 };
  16 reg *list;
  17
  18 static int
  19 get(const char *name)
  20 {
  21   for (reg *iter = list; iter; iter = iter->next)
  22     if (!strcmp (iter->name, name))
  23       return iter->value;
  24   reg *r = calloc (1, sizeof *r);
  25   strcpy (r->name, name); // safe because of max name
  26   r->next = list;
  27   list = r;
  28   return 0;
  29 }
  30
  31 static int
  32 set(const char *name, int adjust)
  33 {
  34   if (getenv ("DEBUG"))
  35     printf(" adjusting %s by %d\n", name, adjust);
  36   for (reg *iter = list; iter; iter = iter->next)
  37     if (!strcmp (iter->name, name)) {
  38       iter->value += adjust;
  39       return iter->value;
  40     }
  41   reg *r = calloc (1, sizeof *r);
  42   strcpy (r->name, name); // safe because of max name
  43   r->value = adjust;
  44   r->next = list;
  45   list = r;
  46   return adjust;
  47 }
  48
  49 int main(void)
  50 {
  51   char d[MAXNAME], s[MAXNAME], dir, op[3];
  52   int adjust, v;
  53   int count = 0;
  54   int high = 0;
  55   // ugly, but works because our data is sane
  56   while (scanf("%3[a-z] %c%*[ne]c %d if %3[a-z] %2[><!=] %d\n",
  57                d, &dir, &adjust, s, op, &v) == 6) {
  58     switch (dir) {
  59     case 'i':
  60       break;
  61     case 'd':
  62       adjust = -adjust;
  63       break;
  64     default:
  65       return 2;
  66     }
  67     int r = get (s);
  68     if (getenv("DEBUG"))
  69       printf("%s %d if %s (%d) %s %d\n", d, adjust, s, r, op, v);
  70     count++;
  71     int doit = 0;
  72     switch (op[0] + op[1]) {
  73     case '>':
  74       if (r > v)
  75         doit = 1;
  76       break;
  77     case '<':
  78       if (r < v)
  79         doit = 1;
  80       break;
  81     case '>' + '=':
  82       if (r >= v)
  83         doit = 1;
  84       break;
  85     case '<' + '=':
  86       if (r <= v)
  87         doit = 1;
  88       break;
  89     case '=' + '=':
  90       if (r == v)
  91         doit = 1;
  92       break;
  93     case '!' + '=':
  94       if (r != v)
  95         doit = 1;
  96       break;
  97     default:
  98       return 3;
  99     }
 100     if (doit) {
 101       v = set(d, adjust);
 102       if (v > high)
 103         high = v;
 104     }
 105   }
 106   printf("parsed %d lines\n", count);
 107   int max = 0;
 108   for (reg *iter = list; iter; iter = iter->next)
 109     if (iter->value > max)
 110       max = iter->value;
 111   printf("largest register contains %d\n", max);
 112   printf("largest value seen %d\n", high);
 113   return 0;
 114 }