# LeetCode 236. Lowest Common Ancestor of a Binary Tree in F#

## URL

leetcode.com/problems/lowest-common-ancesto..

## Code

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

```
type Tree =
| Leaf
| Node of int * Tree * Tree
let lowestCommonAncestor (root: Tree) (p: int) (q: int) : int =
let rec collectAncestors node target acc =
match node with
| Leaf -> [], false
| Node (v, left, right) ->
let acc' = v :: acc
if v = target then
acc' |> List.rev, true
else
match collectAncestors left target acc' with
| acc'', true -> acc'', true
| _, _ -> collectAncestors right target acc'
let rec lowestCommonAncestor' ps qs prev =
match ps, qs with
| h1 :: t1, h2 :: t2 ->
if h1 = h2 then
lowestCommonAncestor' t1 t2 h1
else
prev
| _, _ -> prev
let pAncestors, _ = collectAncestors root p []
let qAncestors, _ = collectAncestors root q []
lowestCommonAncestor' pAncestors qAncestors -1
```