Re^2: Finding repeat sequences.

[sundialsvc4]

It might even be easier than this ... (pseudocode this time)

for $t from 1 to int(length(string) / 2):
  next unless the first $t chars equal the last $t;
  # i.e. "$t" must be a plausible tail-size.

  $r = length - $t;
  
  $incr = int($r / 2);
  while( $incr > 0) {
     next unless ($incr % $r == 0);
     # i.e. must be a possible repeated-block size in this space
     solution is found if string(0, $incr) eq string($incr, $incr);
     # i.e. if we find one repetition then it must be the answer.
     $incr--;
  }
}

As before, start by looking for a tail. If you think you found one, look for repetitions in possibly-sized increments of the remaining string. This approach will consider all successively-larger candidates for the "tail," up to and including the largest tail, which is "half of it." For each tail-size, it looks for one repetition of all possible sizes which would fit evenly within this area, knowing that the left-hand portion is defined to consist only of repetitions. Continue for all tail-sizes, and for each of these, all rep-sizes, until the first success is found. It works only for data which does, in fact, match this assertion.