<h2 id="heading-url">URL</h2>
<p><a href="https://leetcode.com/problems/validate-binary-search-tree/" class="autolinkedURL autolinkedURL-url" target="_blank">leetcode.com/problems/validate-binary-searc..</a></p>
<h2 id="heading-code">Code</h2>
<p><a href="https://github.com/syohex/dotnet-study/blob/master/fsharp/leetcode/problems/0098/main.fsx" class="autolinkedURL autolinkedURL-url" target="_blank">github.com/syohex/dotnet-study/blob/master/..</a></p>
<pre><code class="lang-fsharp">open System

type Tree =
    | Leaf
    | Node of int64 * Tree * Tree

let isValidBST (root: Tree) : bool =
    let rec isValidBST' node (min: int64) (max: int64) =
        match node with
        | Leaf -&gt; true
        | Node (v, left, right) -&gt;
            if v &lt;= min || v &gt;= max then
                false
            else
                isValidBST' left min v &amp;&amp; isValidBST' right v max

    isValidBST' root Int32.MinValue Int32.MaxValue
</code></pre>


## URL

https://leetcode.com/problems/validate-binary-search-tree/

## Code

https://github.com/syohex/dotnet-study/blob/master/fsharp/leetcode/problems/0098/main.fsx

```fsharp
open System

type Tree =
    | Leaf
    | Node of int64 * Tree * Tree

let isValidBST (root: Tree) : bool =
    let rec isValidBST' node (min: int64) (max: int64) =
        match node with
        | Leaf -> true
        | Node (v, left, right) ->
            if v <= min || v >= max then
                false
            else
                isValidBST' left min v && isValidBST' right v max

    isValidBST' root Int32.MinValue Int32.MaxValue
```

LeetCode 98. Validate Binary Search Tree in F#

URL

Code