Orderings Defined by a PQ Tree

• Given a PQ tree T the orderings defined by T is

  • PQ(T) ={F(T’) : T’ is equivalent to T}

A

C

F

E

D

B

T

There are 6 x 2 x 2 = 24 distinct

orderings in PQ(T).

Generally, if a PQ tree T has q Q

node and p P nodes with number

of children c1, c2, ... , cp, then the

number of orderings in PQ(T) is

2q c1! c2! ... cp!.

n! = 1 x 2 x ... x n

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