2016/advent1.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
   8 typedef enum dir {
   9   N,
  10   E,
  11   S,
  12   W,
  13 } dir;
  14
  15 #define BASE 220
  16 bool grid[2*BASE][2*BASE]; // cheat: size it by analysis done in part 1
  17 int x = BASE, y = BASE;
  18
  19 void travel(int dx, int dy, int n)
  20 {
  21   static bool found;
  22   while (n--) {
  23     x += dx;
  24     y += dy;
  25     if (grid[x][y] && !found) {
  26       found = true;
  27       printf ("revisiting spot %d,%d, distance of %d\n", x - BASE, y - BASE,
  28               abs (x - BASE) + abs (y - BASE));
  29     }
  30     grid[x][y] = true;
  31   }
  32 }
  33
  34 int main(void)
  35 {
  36   dir d = N;
  37   char c;
  38   int l;
  39   int maxx = BASE, minx = BASE, maxy = BASE, miny = BASE;
  40   grid[x][y] = true;
  41   while (scanf ("%c%d, ", &c, &l) == 2) {
  42     if (c == 'R')
  43       d++;
  44     else
  45       d--;
  46     switch (d % 4) {
  47     case N:
  48       travel (0, 1, l);
  49       if (y > maxy)
  50         maxy = y;
  51       break;
  52     case E:
  53       travel (1, 0, l);
  54       if (x > maxx)
  55         maxx = x;
  56       break;
  57     case S:
  58       travel (0, -1, l);
  59       if (y < miny)
  60         miny = y;
  61       break;
  62     case W:
  63       travel (-1, 0, l);
  64       if (x < minx)
  65         minx = x;
  66       break;
  67     }
  68   }
  69   printf ("final distance is %d\n", abs (x - BASE) + abs (y - BASE));
  70   printf ("grid size x=%d to %d y=%d to %d\n", minx - BASE, maxx - BASE,
  71           miny - BASE, maxy - BASE);
  72   return 0;
  73 }