I was recently asked this question in my Google screening which I could not answer and the question is like this given a number 'N' find the number of balanced binary tree if one node is not distinguishable from the other( As in the arrangement of nodes does not matter). This is a balanced binary tree and not a BST. Could someone give an insight on how to go about it. The interviewer suggested that it could be derived from the BST solution if you know the DP approach.

I came up with the approach of all the levels filled except for the last level and arranging the remaining nodes on the last level but that does not work in the following case:

		```
				   1
				/.     \
			1.           1
		/       \.       /
	1            1.  1
	/.
1