<h2 id="heading-url">URL</h2>
<p><a target="_blank" href="https://leetcode.com/problems/number-of-beautiful-pairs/description/">Number of Beautiful Pairs - LeetCode</a></p>
<h2 id="heading-code">Code</h2>
<p><a target="_blank" href="https://github.com/syohex/dotnet-study/tree/master/fsharp/leetcode/problems/2748/main.fsx">https://github.com/syohex/dotnet-study/tree/master/fsharp/leetcode/problems/2748/main.fsx</a></p>
<pre><code class="lang-plaintext">open System

let countBeautifulPairs (nums: int list) : int =
    let rec gcd a b = if a % b = 0 then b else gcd b (a % b)

    let rec countBeautifulPairs' pairs acc =
        match pairs with
        | []
        | _ :: [] -&gt; acc
        | (first, _) :: t -&gt;
            let count = t |&gt; List.filter (fun (_, last) -&gt; gcd first last = 1) |&gt; List.length
            countBeautifulPairs' t (acc + count)

    let charToInt = Char.GetNumericValue &gt;&gt; int

    let pairs =
        nums
        |&gt; List.map string
        |&gt; List.map (fun s -&gt; Seq.head s |&gt; charToInt, Seq.last s |&gt; charToInt)

    countBeautifulPairs' pairs 0
</code></pre>


## URL

[Number of Beautiful Pairs - LeetCode](https://leetcode.com/problems/number-of-beautiful-pairs/description/)

## Code

[https://github.com/syohex/dotnet-study/tree/master/fsharp/leetcode/problems/2748/main.fsx](https://github.com/syohex/dotnet-study/tree/master/fsharp/leetcode/problems/2748/main.fsx)

```plaintext
open System

let countBeautifulPairs (nums: int list) : int =
    let rec gcd a b = if a % b = 0 then b else gcd b (a % b)

    let rec countBeautifulPairs' pairs acc =
        match pairs with
        | []
        | _ :: [] -> acc
        | (first, _) :: t ->
            let count = t |> List.filter (fun (_, last) -> gcd first last = 1) |> List.length
            countBeautifulPairs' t (acc + count)

    let charToInt = Char.GetNumericValue >> int

    let pairs =
        nums
        |> List.map string
        |> List.map (fun s -> Seq.head s |> charToInt, Seq.last s |> charToInt)

    countBeautifulPairs' pairs 0
```

LeetCode 2748. Number of Beautiful Pairs in F#

URL

Code