<h2 id="heading-url">URL</h2>
<a target="_blank" href="https://leetcode.com/problems/find-the-duplicate-number/">https://leetcode.com/problems/find-the-duplicate-number/</a>
<h2 id="heading-code">Code</h2>
<a target="_blank" href="https://github.com/syohex/dotnet-study/tree/master/fsharp/leetcode/challenge/202309/find_the_duplicate_number/main.fsx">https://github.com/syohex/dotnet-study/tree/master/fsharp/leetcode/challenge/202309/find_the_duplicate_number/main.fsx</a>
<pre><code class="lang-fsharp">let findDuplicate (nums: int list) : int =
 let rec findDuplicate' nums left right ret =
 if left &gt; right then
 ret
 else
 let mid = left + (right - left) / 2
 let count = nums |&gt; List.filter (fun num -&gt; num &lt;= mid) |&gt; List.length

 if count &gt; mid then
 findDuplicate' nums left (mid - 1) mid
 else
 findDuplicate' nums (mid + 1) right ret

 findDuplicate' nums 1 (nums.Length - 1) 0
</code></pre>

## URL

[https://leetcode.com/problems/find-the-duplicate-number/](https://leetcode.com/problems/find-the-duplicate-number/)

## Code

[https://github.com/syohex/dotnet-study/tree/master/fsharp/leetcode/challenge/202309/find\_the\_duplicate\_number/main.fsx](https://github.com/syohex/dotnet-study/tree/master/fsharp/leetcode/challenge/202309/find_the_duplicate_number/main.fsx)

```fsharp
let findDuplicate (nums: int list) : int =
 let rec findDuplicate' nums left right ret =
 if left > right then
 ret
 else
 let mid = left + (right - left) / 2
 let count = nums |> List.filter (fun num -> num <= mid) |> List.length

 if count > mid then
 findDuplicate' nums left (mid - 1) mid
 else
 findDuplicate' nums (mid + 1) right ret

 findDuplicate' nums 1 (nums.Length - 1) 0
```

LeetCode 287. Find the Duplicate Number

URL

Code