Level codes:

  LEVEL 2     AAJIHGDDC
  LEVEL 3     CGGHDGGDG
  LEVEL 4     HDICICCII
  LEVEL 5     IDHEHDGCC
  LEVEL 6     IJIIDIHEC
  LEVEL 7     CFDFEFEFJ
  LEVEL 8     JIIJIIIIC
  LEVEL 9     AAAABAAAA
  LEVEL 10    CCGDGBBBB
  LEVEL 11    HHIAAJJIG
  LEVEL 12    GGDDJJHFD
  LEVEL 13    JIECBFGFF
  LEVEL 14    HGGEDDCCB
  LEVEL 15    HHHGFGDCC
  LEVEL 16    IHDCHGHFF
  LEVEL 17    IHDCHGHFF
  LEVEL 18    IHDCHGHFF
  LEVEL 19    IHDCHGHFF
  LEVEL 20    IHDCHGHFF