/*
 * Generates resistor network input files for finite approximations to
 *  the infinite network in xkcd #356, Nerd Sniping.  The networks are
 *  even-x-odd size; the size is given by a command-line argument,
 *  which is half the even size and must be at least 1.  A
 *  commandline argument of 1 generates a 2x3-node network
 *
 *	 *---*--(*)
 *	 |   |   |
 *	(*)--*---*
 *
 *  and an argument of 2 generates a 4x5-node network
 *
 *	 *---*---*---*---*
 *	 |   |   |   |   |
 *	 *---*---*--(*)--*
 *	 |   |   |   |   |
 *	 *--(*)--*---*---*
 *	 |   |   |   |   |
 *	 *---*---*---*---*
 *
 *  etc.
 *
 * Node names are of the form X,Y where X and Y are single characters
 *  if the odd dimension is no larger than 36, double characters above
 *  that.  (The program errors out if the argument is so large that the
 *  odd dimension exceeds 36*36=1296.)
 */

#include <stdio.h>
#include <stdlib.h>

extern const char *__progname;

static int n;

static void handleargs(int ac, char **av)
{
 unsigned long int nl;
 char *ep;

 if (ac != 2)
  { fprintf(stderr,"Usage: %s half-size\nhalf-size must be 1 to 647.\n",__progname);
    exit(1);
  }
 nl = strtoul(av[1],&ep,0);
 if ((ep == av[1]) || *ep)
  { fprintf(stderr,"%s: invalid number `%s'\n",__progname,av[1]);
    exit(1);
  }
 n = nl;
 if ((n < 0) || (n != nl) || (n > 647))
  { fprintf(stderr,"%s: out-of-range argument `%s' (must be 1 to 647)\n",__progname,av[1]);
    exit(1);
  }
}

static void print_n(int v)
{
 static const char digs[36] = "0123456789abcdefghijklmnopqrstuvwxyz";

 if (n > 17)
  { if ((v < 0) || (v >= 36*36)) abort();
    printf("%c%c",digs[v/36],digs[v%36]);
  }
 else
  { if ((v < 0) || (v >= 36)) abort();
    printf("%c",digs[v]);
  }
}

static void print_resistor(int x1, int y1, int x2, int y2)
{
 printf("R ");
 print_n(x1);
 printf(",");
 print_n(y1);
 printf(" ");
 print_n(x2);
 printf(",");
 print_n(y2);
 printf(" 1\n");
}

static void print_voltage(int x, int y, int v)
{
 printf("V ");
 print_n(x);
 printf(",");
 print_n(y);
 printf(" %d\n",v);
}

static void gen(void)
{
 int i;
 int j;

 for (i=n+n-1;i>=0;i--)
  { for (j=n+n;j>=0;j--)
     { if (j > 0) print_resistor(j-1,i,j,i);
       if (i > 0) print_resistor(j,i-1,j,i);
     }
  }
 print_voltage(n-1,n,0);
 print_voltage(n+1,n-1,1);
}

int main(int ac, char **av)
{
 handleargs(ac,av);
 gen();
 return(0);
}