1.

Let T(n) be the number of different binary search trees on n distinct elements.Then , where x is(A) n-k+1(B) n-k(C) n-k-1(D) n-k-2

Answer» Answer: (B)
Explanation: The idea is to make a key root, put (k-1) keys in one subtree and remaining n-k keys in other subtree.

A Binary Search Tree (BST) is a tree in which all the nodes follow the below-mentioned properties −

  • The left sub-tree of a node has a key less than or equal to its parent node’s key.
  • The right sub-tree of a node has a key greater than to its parent node’s key.

Now construction binary search trees from n distinct number-
Lets for simplicity consider n distinct numbers as first n natural numbers (starting from 1)
If n=1 We have only one possibility, therefore only 1 BST.
If n=2 We have 2 possibilities , when smaller number is root and bigger number is the right child or second when the bigger number is root and smaller number as left child.

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If n=3 We have 5 possibilities. Keeping each number first as root and then arranging the remaining 2 numbers as in case of n=2.

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