c3算法

# L(G) = [G] + [O]
#   G  = [O]
#      =  GO
# L[E] = EO
# L[F] = [F] + [GO]
# F    = [GO]
#      = FGO
# L[B] = [B] + [FGO]
#   B  = [FGO]
#   BF = [GO]
#   BFG= [O]
#      = BFGO
# L[C] = [C] + [EO]
#   C  = [EO]
#   CE = [O]
#      = CEO
# L[D] = [D] + [GO]
#   D  = [GO]
#   DG = [O]
#      = DGO
# L[A] = [A] + [BFGO] + [CEO] + [DGO]
#   A  = [BFGO] + [CEO] + [DGO]
#   AB = [FGO] + [CEO] + [DGO]
#   ABF= [GO] + [CEO] + [DGO]
#  ABFC= [GO] + [EO] + [DGO]
# ABFCE= [GO] + [O] + [DGO]
# ABFCED = [GO] + [O] + [GO]
# ABFCEDG= [O] + [O] + [O]
#      = ABFCEDGO

# L[G] = GO
# L[D] = DO
# L[E] = EGO
# L[F] = FO
# L[B] = [B] + [DO] + [EGO]
# B    = [DO] + [EGO]
# BD   = [O] + [EGO]
# BDE  = [O] + [GO]
# BDEG = [O] + [O]
#      = BDEGO
# L[C] = [C] + [DO] + [FO]
#   C  = [DO] + [FO]
#   CD = [O] + [FO]
#   CDF= [O] + [O]
#      = CDFO
# L[A] = [A] + [BDEGO] + [CDFO]
# A    = [BDEGO] + [CDFO]
# AB   = [DEGO] + [CDFO]
# ABC  = [DEGO] + [DFO]
# ABCD = [EGO] + [FO]
# ABCDE= [GO] + [FO]
# ABCDEG= [O] + [FO]
# ABCDEGF= [O] + [O]
#      = ABCDEGFO