# LeetCode 637. Average of Levels in Binary Tree in F#

## URL

leetcode.com/problems/average-of-levels-in-..

## Code

github.com/syohex/dotnet-study/blob/master/..

```
type Tree =
| Leaf
| Node of int * Tree * Tree
let averageOfLevels (root: Tree) : double list =
let rec averageOfLevels' node level acc =
match node with
| Leaf -> acc
| Node (v, left, right) ->
let acc' =
match Map.tryFind level acc with
| None -> Map.add level (v, 1) acc
| Some ((sum, count)) -> Map.add level (sum + v, count + 1) acc
let acc'' = averageOfLevels' left (level + 1) acc'
averageOfLevels' right (level + 1) acc''
let m = averageOfLevels' root 0 Map.empty
let max =
m
|> Map.fold (fun acc k _ -> System.Math.Max(acc, k)) 0
seq { 0 .. max }
|> Seq.map (fun i ->
let sum, count = Map.find i m
(double sum) / (double count))
|> Seq.toList
```