How can I find all of the permutations consisting of 1 element from a variable number of arrays of variable length?

Question

I have an array U of arrays D that vary in length. I need to be able to return all permutations of array indices that would select a different perm

Answer 1

To tack on to what Anon said, you don't just loop over them. You maintain state in your class so that you know what your last index was for each array. The logic is the same, but you don't run in a continuous loop. The pseudo-code logic would be:

get_next()
{
  oldn3 = this.n3;
  oldn2 = this.n2;
  oldn1 = this.n1;

  if(this.n3 == this.a3.Count)
     this.n3 = 0;
  else
     this.n3++;

  if(oldn3 > this.n3)
    if(this.n2 == this.a2.Count)
      this.n2 = 0;
    else
      this.n2++;

  if(oldn2 > this.n2)
    if(this.n1 == this.a1.Count)
      this.n1 = 0;
    else
      this.n1++;

  if(oldn1 > this.n1)
    return NO_MORE_PERMS;

  return [n1,n2,n3];  
}

getCurrent()
{
  return [n1,n2,n3];
}