Count unique BSTs.

Hard

0/120

Average time to solve is 15m

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18 upvotes

Asked in company

Problem statement

You have been given a number ‘NUM’. Your task is to count total structurally unique binary search trees from keys 1 to ‘NUM’ considering we should use each key from 1 to ‘NUM’ only once.

Two binary search trees are different if there is at least one node during traversal which is different in values or present in one tree but not present in another tree.

Note:

The answer can be large, hence the return answer % ‘MOD’, where ‘MOD’ is a large prime number (10^9 + 7).

Detailed explanation ( Input/output format, Notes, Images )

Input format :

The first line contains a single integer ‘T’ representing the number of test cases.

The first line of each test case will contain a single integer ‘NUM’ where ‘NUM’ represents the number of keys.

Output Format :

For each test case, print a single line containing the count of total structurally unique binary search trees.

The output of each test case will be printed in a separate line.

Note:

You don’t need to print anything; It has already been taken care of. Just implement the given function.

Constraints:

1 <= T <= 100   
1 <= NUM <= 500

Time limit: 1 sec

Sample Input 1:

2
2
1

Sample Output 1:

2
1

Explanation of sample input 1:

In the first test case, 2 unique BST are possible.

In the second test case, only 1 tree is possible.

Sample Input 2:

2
3
4

Sample Output 2:

5
14

Explanation of sample input 2:

In the first test case, 5 unique BST are possible.

In the second test case, similar to the above way, 14 unique BST are possible.

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