<h2 id="heading-url">URL</h2>
<p><a target="_blank" href="https://leetcode.com/problems/valid-parentheses/description/">Valid Parentheses - LeetCode</a></p>
<h2 id="heading-code">Code</h2>
<p><a target="_blank" href="https://github.com/syohex/dotnet-study/tree/master/fsharp/leetcode/challenge/202304/valid_parentheses/main.fsx">https://github.com/syohex/dotnet-study/tree/master/fsharp/leetcode/challenge/202304/valid_parentheses/main.fsx</a></p>
<pre><code class="lang-plaintext">let isValid (s: string) : bool =
    let rec isValid' cs acc =
        match cs with
        | [] -&gt;
            match acc with
            | [] -&gt; true
            | _ -&gt; false
        | h :: t -&gt;
            match h with
            | '('
            | '['
            | '{' -&gt; isValid' t (h :: acc)
            | ')' -&gt;
                match List.tryHead acc with
                | Some(v) when v = '(' -&gt; isValid' t (List.tail acc)
                | _ -&gt; false
            | ']' -&gt;
                match List.tryHead acc with
                | Some(v) when v = '[' -&gt; isValid' t (List.tail acc)
                | _ -&gt; false
            | '}' -&gt;
                match List.tryHead acc with
                | Some(v) when v = '{' -&gt; isValid' t (List.tail acc)
                | _ -&gt; false
            | _ -&gt; failwith "never reach here"

    isValid' (Seq.toList s) []
</code></pre>


## URL

[Valid Parentheses - LeetCode](https://leetcode.com/problems/valid-parentheses/description/)

## Code

[https://github.com/syohex/dotnet-study/tree/master/fsharp/leetcode/challenge/202304/valid\_parentheses/main.fsx](https://github.com/syohex/dotnet-study/tree/master/fsharp/leetcode/challenge/202304/valid_parentheses/main.fsx)

```plaintext
let isValid (s: string) : bool =
    let rec isValid' cs acc =
        match cs with
        | [] ->
            match acc with
            | [] -> true
            | _ -> false
        | h :: t ->
            match h with
            | '('
            | '['
            | '{' -> isValid' t (h :: acc)
            | ')' ->
                match List.tryHead acc with
                | Some(v) when v = '(' -> isValid' t (List.tail acc)
                | _ -> false
            | ']' ->
                match List.tryHead acc with
                | Some(v) when v = '[' -> isValid' t (List.tail acc)
                | _ -> false
            | '}' ->
                match List.tryHead acc with
                | Some(v) when v = '{' -> isValid' t (List.tail acc)
                | _ -> false
            | _ -> failwith "never reach here"

    isValid' (Seq.toList s) []
```

LeetCode 20. Valid Parentheses in F#

URL

Code