2017/advent11.c

   1 #define _GNU_SOURCE 1
   2 #include <stdio.h>
   3 #include <string.h>
   4 #include <stdlib.h>
   5 #include <unistd.h>
   6
   7 int distance(int nw, int n, int ne) {
   8   // rotating path so all steps are positive results in same distance...
   9   while (nw < 0 || n < 0 || ne < 0) {
  10     int tnw = -ne, tn = nw, tne = n;
  11     nw = tnw;
  12     n = tn;
  13     ne = tne;
  14   }
  15   if (nw < ne) {
  16     n += nw;
  17     ne -= nw;
  18     nw = 0;
  19   } else {
  20     n += ne;
  21     nw -= ne;
  22     ne = 0;
  23   }
  24   return nw + n + ne;
  25 }
  26
  27 int main(int argc, char **argv)
  28 {
  29   if (argc != 2)
  30     return 1;
  31   int nw = 0, n = 0, ne = 0;
  32   char *p = argv[1];
  33   char *next = p;
  34   int count = 0;
  35   int max = 0, dist = 0;
  36   while (*next && (next = strchrnul(p, ','))) {
  37     count++;
  38     if ((next - p) == 1)
  39       n += *p == 'n' ? 1 : -1;
  40     else if (p[1] == 'e')
  41       if (*p == 'n')
  42         ne++;
  43       else
  44         nw--;
  45     else if (*p == 'n')
  46       nw++;
  47     else
  48       ne--;
  49     dist = distance(nw, n, ne);
  50     if (max < dist)
  51       max = dist;
  52     p = next + 1;
  53   }
  54   printf("after %d steps, nw=%d n=%d ne=%d\n", count, nw, n, ne);
  55   printf("max distance %d, final distance %d\n", max, dist);
  56   return 0;
  57 }