<h2 id="heading-url">URL</h2>
<a target="_blank" href="https://leetcode.com/problems/find-mode-in-binary-search-tree/description/?envType=daily-question&amp;envId=2023-11-01">Find Mode in Binary Search Tree - LeetCode</a>
<h2 id="heading-code">Code</h2>
<a target="_blank" href="https://github.com/syohex/dotnet-study/tree/master/fsharp/leetcode/problems/0501/main.fsx">https://github.com/syohex/dotnet-study/tree/master/fsharp/leetcode/problems/0501/main.fsx</a>
<pre><code class="lang-fsharp">open System

type Tree =
 | Leaf
 | Node of int * Tree * Tree

let findMode (root: Tree) : int list =
 let rec nodeFreq node acc =
 match node with
 | Leaf -&gt; acc
 | Node(v, left, right) -&gt;
 let acc' =
 match Map.tryFind v acc with
 | Some(n) -&gt; Map.add v (n + 1) acc
 | None -&gt; Map.add v 1 acc

 let acc'' = nodeFreq left acc'
 nodeFreq right acc''

 let freq = nodeFreq root Map.empty
 let mode = Map.fold (fun acc _ (v: int) -&gt; Math.Max(acc, v)) -1 freq
 freq |&gt; Map.fold (fun acc k v -&gt; if v = mode then k :: acc else acc) []
</code></pre>

## URL

[Find Mode in Binary Search Tree - LeetCode](https://leetcode.com/problems/find-mode-in-binary-search-tree/description/?envType=daily-question&envId=2023-11-01)

## Code

[https://github.com/syohex/dotnet-study/tree/master/fsharp/leetcode/problems/0501/main.fsx](https://github.com/syohex/dotnet-study/tree/master/fsharp/leetcode/problems/0501/main.fsx)

```fsharp
open System

type Tree =
    | Leaf
    | Node of int * Tree * Tree

let findMode (root: Tree) : int list =
    let rec nodeFreq node acc =
        match node with
        | Leaf -> acc
        | Node(v, left, right) ->
            let acc' =
                match Map.tryFind v acc with
                | Some(n) -> Map.add v (n + 1) acc
                | None -> Map.add v 1 acc

            let acc'' = nodeFreq left acc'
            nodeFreq right acc''

    let freq = nodeFreq root Map.empty
    let mode = Map.fold (fun acc _ (v: int) -> Math.Max(acc, v)) -1 freq
    freq |> Map.fold (fun acc k v -> if v = mode then k :: acc else acc) []
```

LeetCode 501. Find Mode in Binary Search Tree in F#

URL

Code