post order

Question

the number of binary trees with 3 nodes which when traversed in post order gives the sequence a,b,c

is

a)3  b)9 c)7 d)5

Answer 1

I think 5 and trees are 

Postorder : Left Right Root

Since C is last in given postoder

In post order root is last So C root of trees 

A and B are placed so that ABC is postorder to make that either A is child of B or Left sibiling of B whose root is C

Comments

Same question but instead of "post-order" what if there is"Pre-order"?

Answer 2

in order to get abc sequence their will be 5 binary tree possible . for that firstly u draw all unlabel binary tree and then fill accordingly by which u got postorder abc so here ans is d

Comments

What if it is preorder instead of post order ? Will answer be same ?