4 ms·

improved, gives 80 ^(x|(xx){1,9}|x{32}|(x{64})+)$

• rplnt 13y ago
  I tried to get rid of those redundant ^ and $ but it somehow didn't work. I probably forgot to put it all inside one group.
  • alanh 13y ago
    They are not redundant. Any string of one or more exes is going to constrain a substring of exes of length 2^n (consider n=0 for a trivial proof), so you do need those anchors!
    • rplnt 13y ago
      I meant my previous post where I had them in every single possibility.