# LeetCode 958. Check Completeness of a Binary Tree in F#

## URL

Check Completeness of a Binary Tree - LeetCode

## Code

https://github.com/syohex/dotnet-study/tree/master/fsharp/leetcode/problems/0958/main.fsx

```
type Tree =
| Leaf
| Node of int * Tree * Tree
let isCompleteTree (root: Tree) : bool =
let rec countNodes node =
match node with
| Leaf -> 0
| Node(_, left, right) -> 1 + (countNodes left) + (countNodes right)
let rec isCompleteTree' q nodes =
match q with
| [] -> true
| _ ->
let valid =
q
|> List.forall (fun (node, index) ->
match node with
| Leaf -> true
| _ -> index <= nodes)
if valid then
let q' =
q
|> List.fold
(fun acc (node, index) ->
match node with
| Leaf -> acc
| Node(_, left, right) -> (left, 2 * index) :: (right, 2 * index + 1) :: acc)
[]
isCompleteTree' q' nodes
else
false
isCompleteTree' [ (root, 1) ] (countNodes root)
```