已知
child parent a b a c d b d c b e b f c g c h x g x h m x m n o x o n
则
c 2+c+g 2+c+h 1+a+c 1+d+c h 1+c+h 1+x+h d 2+d+b 2+d+c b 1+a+b 1+d+b 2+b+e 2+b+f o 2+o+x 2+o+n e 1+b+e m 2+m+x 2+m+n x 2+x+g 2+x+h 1+m+x 1+o+x a 2+a+c 2+a+b
也即
gc[0] = a gc[1]=d gp[0] = g gp[1] = h gc[0] = a gc[1]=d gp[0] = e gp[1] = f gc[0] = m gc[1]=o gp[0] = g gp[1] = h
则
grandchild grandparent a g a h d g d h a e a f d e d f m g m h o g o h