ISRO | ISRO CS 2011 | Question 11

How many distinct binary search trees can be created out of 4 distinct keys?
(A) 5
(B) 14
(C) 24
(D) 35


Answer: (B)

Explanation: Distinct binary search trees that can be created out of 4 distinct keys can be found out using the Catalon number.
Catalon number = (2n)!/(n! * (n+1)!)
Here n = 4,
Number of distinct BST’s = (4 x 2)! / (4! x 5!) = 14
So, correct option is (B)

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