<p>You have a set of integers <code>s</code>, which originally contains all the numbers from <code>1</code> to <code>n</code>. Unfortunately, due to some error, one of the numbers in <code>s</code> got duplicated to another number in the set, which results in <strong>repetition of one</strong> number and <strong>loss of another</strong> number.</p>

<p>You are given an integer array <code>nums</code> representing the data status of this set after the error.</p>

<p>Find the number that occurs twice and the number that is missing and return <em>them in the form of an array</em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<pre><strong>Input:</strong> nums = [1,2,2,4]
<strong>Output:</strong> [2,3]
</pre><p><strong class="example">Example 2:</strong></p>
<pre><strong>Input:</strong> nums = [1,1]
<strong>Output:</strong> [1,2]
</pre>
<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>2 &lt;= nums.length &lt;= 10<sup>4</sup></code></li>
	<li><code>1 &lt;= nums[i] &lt;= 10<sup>4</sup></code></li>
</ul>

#include <unordered_set>
#include <ranges>
#include <algorithm>
#include <utility>

class Solution {
public:
    vector<int> findErrorNums(vector<int>& values) 
    {
        auto inserted_values = std::unordered_set<int>{};
        auto failed_insertion = [&inserted_values](auto value) { return !inserted_values.insert(value).second; };
        auto duplicate = *std::ranges::find_if(values, failed_insertion);

        auto sum = std::ranges::fold_left(values, 0, std::plus<>());
        auto size = std::ssize(values);
        auto expected_sum = size * (size + 1) / 2;
        int missing_value = expected_sum - sum + duplicate;

        return {duplicate, missing_value};
    }
};
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