<h2 id="heading-url">URL</h2>
<p><a href="https://leetcode.com/problems/longest-valid-parentheses/" class="autolinkedURL autolinkedURL-url" target="_blank">leetcode.com/problems/longest-valid-parenth..</a></p>
<h2 id="heading-code">Code</h2>
<p><a href="https://github.com/syohex/dotnet-study/blob/master/fsharp/leetcode/problems/0032/main.fsx" class="autolinkedURL autolinkedURL-url" target="_blank">github.com/syohex/dotnet-study/blob/master/..</a></p>
<pre><code class="lang-fsharp">open System

let longestValidParentheses (s: string) : int =
    let rec longestValidParentheses' cs stack (ret: int) =
        match cs with
        | [] -&gt; ret
        | (i, h) :: t -&gt;
            if h = '(' then
                longestValidParentheses' t (i :: stack) ret
            else
                let stack' =
                    match stack with
                    | [] -&gt; []
                    | _ :: rest -&gt; rest

                match stack' with
                | [] -&gt; longestValidParentheses' t [ i ] ret
                | top :: _ -&gt;
                    let ret' = Math.Max(ret, i - top)
                    longestValidParentheses' t stack' ret'

    let cs = s |&gt; Seq.toList |&gt; List.mapi (fun i c -&gt; i, c)
    longestValidParentheses' cs [ -1 ] 0
</code></pre>


## URL

https://leetcode.com/problems/longest-valid-parentheses/

## Code

https://github.com/syohex/dotnet-study/blob/master/fsharp/leetcode/problems/0032/main.fsx

```fsharp
open System

let longestValidParentheses (s: string) : int =
    let rec longestValidParentheses' cs stack (ret: int) =
        match cs with
        | [] -> ret
        | (i, h) :: t ->
            if h = '(' then
                longestValidParentheses' t (i :: stack) ret
            else
                let stack' =
                    match stack with
                    | [] -> []
                    | _ :: rest -> rest

                match stack' with
                | [] -> longestValidParentheses' t [ i ] ret
                | top :: _ ->
                    let ret' = Math.Max(ret, i - top)
                    longestValidParentheses' t stack' ret'

    let cs = s |> Seq.toList |> List.mapi (fun i c -> i, c)
    longestValidParentheses' cs [ -1 ] 0
```

LeetCode 32. Longest Valid Parentheses in F#

URL

Code