hanoi-9.c

#include <stdio.h>
#include <error.h>

#define DISKS 64

int n[3], tower[3][DISKS];

void display (void)
{
  printf ("\n");
  for (int i = 0; i < 3; i++)
    {
      printf ("tower %d:", i);
      for (int j = 0; j < n[i]; j++)
        printf (" %d", tower[i][j]);
      printf ("\n");
    }
}

void move (int from, int to, int disks)
{
  if (disks == 1)
    {
      if (n[from] <= 0)
        error (1, 0, "trying to move disk from empty tower");
      if (n[to] > 0 && tower[to][n[to] - 1] < tower[from][n[from] - 1])
        error (1, 0, "trying to move larger disk on smaller one");
      tower[to][n[to]] = tower[from][n[from] - 1];
      n[to]++;
      n[from]--;
      static int counter = 1;
      if (counter++ >= 100000000)
        {
          display ();
          counter = 1;
        }
    }
  else
    {
      int help = 0 + 1 + 2 - from - to;
      move (from, help, disks - 1);
      move (from, to, 1);
      move (help, to, disks - 1);
    }
}

int main (void)
{
  n[0] = DISKS;
  for (int i = 0; i < DISKS; i++)
    tower[0][i] = DISKS - i;
  n[1] = 0;
  n[2] = 0;
  display ();
  move (0, 2, DISKS);
  display ();
  return 0;
}