# 99 Elm Problems/Problem 60

60.a) Construct a height-balanced binary trees with a given number of nodes.

Consider a height-balanced binary tree of height H. What is the maximum number of nodes it can contain? Clearly, MaxN = 2**H 1. However, what is the minimum number MinN? This question is more difficult.

60.b) Find the minimum number of nodes in a height-balanced binary tree of height H.

60.c) Find the maximum height H a height-balanced binary tree with N nodes can have. Find out how many height-balanced trees exist for N = 15.

**# # # THIS IS A STUB # # #**

Example in Elm:

```
import Html exposing (text)
import List
f : Int -> Int
-- your implementation goes here
main = text (toString (f 0))
```

Result:

```
4
```